In Tattvārtha Sūtra, the term is usually understood as:

• bhāvanā-saṃvāsaḥ = dwelling in, or remaining in, a mental state / repeated contemplation
• saṃvāsaḥ = association, residing together, intimate contact, or dwelling with

In Jain usage, saṃvāsa generally means constant association or close contact, and bhāvanā-saṃvāsa points to continuous mental dwelling in a particular thought, feeling, or spiritual contemplation.

Simple meaning

• Bhāvanā = भावना = contemplation, reflection, mental cultivation
• Saṃvāsa = साथ रहना / साथ में ठहरना = dwelling, association, staying with

So together it means: “continuously abiding in a particular contemplation or inner disposition.”

In Jain spiritual sense

• staying in auspicious thoughts,
• repeated reflection on truth,
• cultivating right disposition,
• or being deeply associated with a mental state.

If you want, I can also give the exact sutra line and its word-by-word meaning (padārtha) in simple Jain terminology.