adverb, noun which may take the genitive case particle 'no'
Refers to the amount, degree, or extent of something, often implying it is limited or just this much. Can be used adverbially or with の to modify a noun.
これだけあれば十分です。
This much is enough.
これだけの量なら一人で食べられる。
If it's only this amount, I can eat it by myself.
Compound of これ (this) and だけ (only/just), literally 'just this'.