Does Ashiok, Nightmare Weaver's ability exiling cards from a library count as milling?

Milling is a defined game term under CR 701.13: to mill a card means to put the top card of a library into its owner's graveyard. Any effect that sends cards from a library to any other zone — such as exile — is not milling, regardless of how similar it feels.

Ashiok, Nightmare Weaver's +2 loyalty ability exiles the top three cards of target opponent's library face down. Because those cards go to the exile zone rather than the graveyard, this ability does not mill and cannot be interacted with by cards that care about milling (e.g., Tasha's Hideous Laughter, which only counts cards milled into the graveyard).

Conversely, effects that specifically say 'mill' (such as Millstone or Glimpse the Unthinkable) would not interact with Ashiok's ability, and Ashiok's ability would not trigger mill-based payoffs like Ruin Crab or Hedron Crab.

Concrete example: Your opponent controls a Ruin Crab (which triggers whenever you mill one or more cards). You activate Ashiok's +2 ability, exiling the top three cards of their library. Ruin Crab does not trigger, because those cards were exiled, not milled into a graveyard.

Remember: the destination matters. Library → graveyard = mill (CR 701.13). Library → exile = exile, nothing more.