Freeze and Stun are similar effects that both stop an enemy’s movement. They both can only be applied by certain units, although when a unit is frozen, ice appears around them.
Stun can either be applied when a unit attacks or through a manual ability, although the latter is much more common. Manual abilities than can stun units are commonly referred to as “timestops” (as some of them originate from JoJo’s Bizarre Adventure). While a unit is frozen/stunned, they cannot be timestopped.