Ekki is correct. Crowd control refers to having power on what the enemy will do in order to stay the party that is in control. This is not limited to stuns.
Stuns are what's called "hard" CC. Slows, snares, maybe silences and a bunch of others are "soft" CC. Also, Malphite's ult is a knockup (works like a stun but it's not affected by tenacity), which is also hard CC. Other hard CC are taunts/charms and Lulu's polymorph.
CC stands for crowd control. There are three types:
1)soft CC: these are things like a silence, or a slow. So anivias ulti, malphite q, and cass w are examples of soft cc. You can also "buy" soft cc in game by getting items such as rylais or frozen mallet
2)hard CC: These are things that in a way can displace a champion, such as a knockup(malphite ulti) or a push(poppy e). Snares(ivern q, cait traps w i think), lock downs/suppression(warwick ulti), taunts(rammus E) and stuns (annie passive) also count as hard CC. These will all proc the keystone Courage of the colosuss
3)death: "death is the best cc"(this is a joke in case you didn't get it)
To stop your enemies and manipulate the battle using deliberating effects to hamper you enemies offense and set up easier kill's among other things as CC can be incredible versatile and turn the tide of a battle.
Cool down reduction. You can have a maximum of 40% normally, reducing the cool down of all of your abilities (other than summoner spells) by however much you have.
Most of the time it is not important to know what hard CC or soft CC is, but if you take
1)soft CC: these are things like a silence, or a slow. So anivias ulti, malphite q, and cass w are examples of soft cc. You can also "buy" soft cc in game by getting items such as rylais or frozen mallet
2)hard CC: These are things that in a way can displace a champion, such as a knockup(malphite ulti) or a push(poppy e). Snares(ivern q, cait traps w i think), lock downs/suppression(warwick ulti), taunts(rammus E) and stuns (annie passive) also count as hard CC. These will all proc the keystone Courage of the colosuss
3)death: "death is the best cc"(this is a joke in case you didn't get it)