Velvet is a woven fabric with a short dense pile which gives it a luxurious soft feel. Velvets have a good amount of drape. Velvet does not have a natural stretch but can have elastane woven into the fabric to give it some stretch whereas velour is a plush knit fabric that has a natural stretch.
Sequin fabrics normally have individual sequins sewn onto a mesh base. These sequins are normally made out of plastic and therefore aren't biodegradable.
To learn more about velvet and velour fabrics, and tips on how to sew with these fabrics look at our guide