The meaning of Brahman & Vasudeva according to Shreemad Bhagvat Purana.

वदन्ति तत्तत्वविदस्तत्वम् यज्ज्ञानमद्वयम् ।
ब्रह्मेति परमात्मेति भगवानिति शब्द्द्यते ॥ 11

vadanti tat tattva-vidas
tattvaḿ yaj jñānam advayam
brahmeti paramātmeti
bhagavān iti śabdyate

Learned transcendentalists who know the Absolute Truth call this nondual substance Brahman, Paramatma or Bhagavan.SB 1.2.11

So according to Bhagvata the Knowledge or Gyana is called a Tatva. And that non-dual , transcendental knowledge itself is Brahman.People call it by different names.

यत्तत्सत्त्वगुणं स्वच्छं शान्तं भगवतः पदम् । 
यदाहुर्वासुदेवाख्यं चित्तं तन्महदात्मकम् ॥21॥ 

yat tat sattva-guṇaḿ svacchaḿ 
śāntaḿ bhagavataḥ padam 
yad āhur vāsudevākhyaḿ 
cittaḿ tan mahad-ātmakam 

The mode of goodness, which is the clear, sober status of understanding the Personality of Godhead and which is generally called vasudeva, or consciousness, becomes manifest in the mahat-tattva.SB 3.26.21

Purport:  The vāsudeva manifestation is called pure goodness, or śuddha-sattva. In the śuddha-sattva status there is no infringement of the other qualities, namely passion and ignorance. The vāsudeva stage is free from infringement by material desires and is the status in which one can understand the Supreme Personality of Godhead, or the objective which is described in the Bhagavad-gītā as adbhuta.

The meaning of Brahman & Vasudeva according to Shreemad Bhagvat Purana.

वदन्ति तत्तत्वविदस्तत्वम् यज्ज्ञानमद्वयम् ।
ब्रह्मेति परमात्मेति भगवानिति शब्द्द्यते ॥ 11

vadanti tat tattva-vidas
tattvaḿ yaj jñānam advayam
brahmeti paramātmeti
bhagavān iti śabdyate

Learned transcendentalists who know the Absolute Truth call this nondual substance Brahman, Paramatma or Bhagavan.[SB 1.2.11][1]

Here is another translation by [ Motilal Banarsidass][2] Publishers.

Those who possess the knowledge of truth (tattva) call the knowledge of non-duality as the Truth. It is also variously designated as Brahman ,Paramatma or Bhagvan.

So according to Bhagvata Brahman is non-dual entity ,which is absolute truth and that truth tatva is also called as Paramatma or Bhagvan.

यत्तत्सत्त्वगुणं स्वच्छं शान्तं भगवतः पदम् । 
यदाहुर्वासुदेवाख्यं चित्तं तन्महदात्मकम् ॥21॥ 

yat tat sattva-guṇaḿ svacchaḿ 
śāntaḿ bhagavataḥ padam 
yad āhur vāsudevākhyaḿ 
cittaḿ tan mahad-ātmakam 

The mode of goodness, which is the clear, sober status of understanding the Personality of Godhead and which is generally called vasudeva, or consciousness, becomes manifest in the mahat-tattva.[SB 3.26.21][3]

Purport:  The vāsudeva manifestation is called pure goodness, or śuddha-sattva. In the śuddha-sattva status there is no infringement of the other qualities, namely passion and ignorance. The vāsudeva stage is free from infringement by material desires and is the status in which one can understand the Supreme Personality of Godhead, or the objective which is described in the Bhagavad-gītā as adbhuta.

And here is description of Vasudeva from Motilal Banarsidass version.

(It is well known in agamas) that Mahat ,which is characterized by Satva-Guna ,Pure ,free from passion (like love hatred etc.) and the place of supreme lord is citta ,and it is called Vasudeva and is composed of Mahat-Tatva.

So Vasudeva is basically first among four Vyuha's who is supreme Mahat- Tatva ,which is of Satva Guna and seated within as the super soul in Lord’s expansion of 4 Vyuhas. [1]: https://www.vedabase.com/en/sb/1/2/11 [2]: https://archive.org/details/BhagavataPuranaMotilalEnglish [3]: https://www.vedabase.com/en/sb/3/26/21

The meaning of Brahman & Vasudeva according to Shreemad Bhagvat Purana.

वदन्ति तत्तत्वविदस्तत्वम् यज्ज्ञानमद्वयम् ।
ब्रह्मेति परमात्मेति भगवानिति शब्द्द्यते ॥ 11

vadanti tat tattva-vidas
tattvaḿ yaj jñānam advayam
brahmeti paramātmeti
bhagavān iti śabdyate

Learned transcendentalists who know the Absolute Truth call this nondual substance Brahman, Paramatma or Bhagavan.SB 1.2.11

यत्तत्सत्त्वगुणं स्वच्छं शान्तं भगवतः पदम् । 
यदाहुर्वासुदेवाख्यं चित्तं तन्महदात्मकम् ॥21॥ 

yat tat sattva-guṇaḿ svacchaḿ 
śāntaḿ bhagavataḥ padam 
yad āhur vāsudevākhyaḿ 
cittaḿ tan mahad-ātmakam 

The mode of goodness, which is the clear, sober status of understanding the Personality of Godhead and which is generally called vasudeva, or consciousness, becomes manifest in the mahat-tattva.SB 3.26.21

Purport:  The vāsudeva manifestation is called pure goodness, or śuddha-sattva. In the śuddha-sattva status there is no infringement of the other qualities, namely passion and ignorance. The vāsudeva stage is free from infringement by material desires and is the status in which one can understand the Supreme Personality of Godhead, or the objective which is described in the Bhagavad-gītā as adbhuta.

The meaning of Brahman & Vasudeva according to Shreemad Bhagvat Purana.

वदन्ति तत्तत्वविदस्तत्वम् यज्ज्ञानमद्वयम् ।
ब्रह्मेति परमात्मेति भगवानिति शब्द्द्यते ॥ 11

vadanti tat tattva-vidas
tattvaḿ yaj jñānam advayam
brahmeti paramātmeti
bhagavān iti śabdyate

Learned transcendentalists who know the Absolute Truth call this nondual substance Brahman, Paramatma or Bhagavan.SB 1.2.11

So according to Bhagvata the Knowledge or Gyana is called a Tatva. And that non-dual , transcendental knowledge itself is Brahman.People call it by different names.

यत्तत्सत्त्वगुणं स्वच्छं शान्तं भगवतः पदम् । 
यदाहुर्वासुदेवाख्यं चित्तं तन्महदात्मकम् ॥21॥ 

yat tat sattva-guṇaḿ svacchaḿ 
śāntaḿ bhagavataḥ padam 
yad āhur vāsudevākhyaḿ 
cittaḿ tan mahad-ātmakam 

The mode of goodness, which is the clear, sober status of understanding the Personality of Godhead and which is generally called vasudeva, or consciousness, becomes manifest in the mahat-tattva.SB 3.26.21

Purport:  The vāsudeva manifestation is called pure goodness, or śuddha-sattva. In the śuddha-sattva status there is no infringement of the other qualities, namely passion and ignorance. The vāsudeva stage is free from infringement by material desires and is the status in which one can understand the Supreme Personality of Godhead, or the objective which is described in the Bhagavad-gītā as adbhuta.