This is different from the holy basil plant, Ocimum tenuiflorum, which is also called tulsi. The leaves and oil of holy basil are used in Ayurvedic medicine for many purposes, but typically not the seeds.
Sweet basil seeds are a similar size as chia seeds. The difference is basil seeds are completely black and tear-shaped, whereas chia seeds are typically mottled shades of grey with brown and have a more rounded shape.
Like chia, basil seeds become gelatinous when soaked in water. They are used in drinks in many Asian countries for thickening as well as for health.