soft brick

When a phone or other electronic device is rendered entirely unusable ("bricked", ie, the device has the functionality of a brick), but in a non-permanent way, such that with the correct tools and techniques, it can be revived. Contrast with "hard brick" where the device is well and truly useless. The process of unbricking it may still be enough work that one may choose to just get a new one (depending on how expensive it is to replace).

Generally implies that the damage is done to the firmware or software, not the hardware - a phone that was dunked in a fishtank might well be destroyed, but one wouldn't call that "bricked"

"Hey, what happened, I thought you bricked your phone trying to root it the other day - did you get a new one?"

"Oh no, it was just a soft brick. It took me hours to figure out how, but I was able to get it to boot last night and reinstalled android. Lost all my contacts though, and it's still not rooted..."

soft brick

Your phone becomes nearly impossible to use, slower, less functional, and is usually because of a virus or various malware.

Jessie's phone was soft bricked last night.

soft brick

When a phone's system is unusable or not bootable at all, but you can access the recovery or download mode, you can call it a soft brick/it gets soft-bricked. After downloading the original software, it should return to the usable state. It often happens after flashing a custom system.
A hard brick is similar, yet the very opposite. - A hard brick is a literal brick, because the firmware is well fucked up and you cannot even access the download mode.

"flashing" -> Copying/downloading a (custom) system onto an Android phone
"ROM" -> system
"Fastboot/Download mode" -> a mode on an Android phone that allows you to flash files directly into a phone's filesystem

I have a soft bricked phone. I was just going to flash the stock software on it.