Modded meaning modified doesn't refer to all forms of game modifications when refering to minecraft. Mods for minecraft are external additions to minecraft; however, client side modifications such as ease of life clients or cheat clients aren't commonly considered mods.
Players aren't often content with only one mod being active at a time as it usually doesn't add enough to make it fun to play. Modpacks were created to fix this problem. Modpacks are bunches of mods being added together in a cohesive way often changing the way you play the game tremendously. Players made custom launchers that would allow others to play their modpacks more easily. The following are some popular modpacks that were played during the peak of modpacks.
There are lots of other packs, but they weren't as popular.