Activated abilities contain a colon. They’re generally written “[Cost]: [Effect].” Some keywords are activated abilities and will have colons in their reminder text.

Activated abilities of copies of a spell with that name (such as Lightning Storm) cannot be activated.

The named card can be cast face down.

You can name either half of a split card, but not both. If you do so, that half (and both halves, if the split card has fuse) can’t be cast. The other half is unaffected.

Voidstone Gargoyle stops activated abilities that are mana abilities from being activated, unlike Pithing Needle.