TRIM is a standard ATA command. It allows the OS to tell the drive "I've finished with those sectors" without actually performing a write (which is faster, and prolongs the life of the flash memory). The SSD can garbage collect however it sees fit, so there may be performance differences between brands.
Obviously it's only any use if the OS driver and filesystem support it, which all the major ones now do. In the early days of SSDs, appropriate compatibility was a big deal (I've got a 32gig SSD[1] with buggy firmware whose write performance makes low-end spinning rust look fast), but these days they tend to Just Work.
[1] Relegated to boot drive duty in a router, where it matters not a jot.