A Trim command which allows an operating system to inform a solid-state drive (SSD) which blocks of data are no longer considered in use and can be wiped internally.
Trim was introduced soon after SSD’s started to become an affordable alternative to traditional hard disks. Because low-level operation of SSDs differs significantly from hard drives, the typical way in which operating systems handle operations like Erasing, Formatting resulted in unanticipated progressive performance degradation of write operations on SSDs
In other words, TRIM helps to maintain the performance of solid-state drives (SSDs) at an optimal level over the lifetime of the drive.
TRIM functions by actively deleting invalid data from the SSD’s memory cells to ensure that write operations perform at full speed.
Before EL Capitan Trim must be enabled by custom patches for Third-party SSDs
After EL Capitan Apple Supports Trim for Third-party SSDs but it must be enabled manually by the following command