The terminology became mainstream during World of Warcraft. Progression refers to the effort of downing the next boss in the raid. Raid content is normally not easy to clear and takes weeks or months to reach the last boss of the raid and kill it.
This was possible due to each raid group of 40 (later 25) people having their own unique instance of the raid dungeon which would 'save' your progress in that dungeon. Meaning if you killed the first 3 bosses, then all of you left the dungeon and came back the next day, those 3 bosses would still be dead. WoW and similar MMOs resetted all saved instances weekly. This meant guilds had limited time each week to attempt the current boss they were stuck on before a new week starts and they have to kill the earlier bosses again.
Thus in WoW's vanilla version as well as its first expansion, when content was hard and all raids only had 1 difficulty, most guilds were not able to clear the current 'tier' of content before the next tier was introduced (via content patch).
A progression guild aims to fully clear every tier of raid when it is still current. Accomplished guilds usually do so long before the next tier is introduced and are usually very well geared, if not fully geared, in the current tier's gear.
"End Game" in a tiered raiding MMO refers to the large scale raids.
Umbra Sanctum Default replied
624 weeks ago