Full grain
Full grain leather includes the entire grain layer with all its natural imperfections — brands, scars, color variation. It's the most durable and develops the best patina. Specify for family-room sofas and reading chairs that will see decades of use.
Top grain
Top grain has the outer layer sanded and corrected to remove imperfections, then usually finished with a pigment coat. It's more uniform than full grain and slightly less durable. The trade standard for premium leather upholstery — Hancock & Moore uses it almost exclusively.
Split and bonded
Split leather is the lower layers of the hide with a surface coating. Bonded leather is shredded leather mixed with polyurethane. Both degrade faster than top grain and don't age gracefully — avoid specifying them for residential work unless budget is the hard constraint.
What to actually ask the vendor
Ask three questions: Is it top grain? Is it aniline-dyed or pigment-finished? What's the break-in behavior? The answers tell you whether the piece will look great in a month or look tired in a year.