"secure delete" (actually "secure erase") is a term from the ATA standard, it's supported by practically all ATA and later SATA devices for a very long time. The idea was you'd tell the disk to erase everything, it would do the actual deletion in the background but would not allow reading the old data. This was also the way to reset passworded harddrives, you could send a secure erase command without authentication, the drive would wipe itself and once done, the password is gone.
Once SSDs arrived on the scene, they were limited by the interface as ATA didn't specify a way to mark sectors as unused. People found that their performance would degrade with use as all the sectors became utilized. But a secure erase command would mark all sectors as erased, so the drive would work like new. Later on, ATA got the TRIM (and later queued versions of TRIM) so the OS can mark specific sectors as erased. But the result is that a lot of people confuse flash sector erasing with secure erase.
Once SSDs arrived on the scene, they were limited by the interface as ATA didn't specify a way to mark sectors as unused. People found that their performance would degrade with use as all the sectors became utilized. But a secure erase command would mark all sectors as erased, so the drive would work like new. Later on, ATA got the TRIM (and later queued versions of TRIM) so the OS can mark specific sectors as erased. But the result is that a lot of people confuse flash sector erasing with secure erase.