This is the 4473rd most frequent German word.
lachen
"To laugh."
The verb 'lachen' is used as an infinitive to denote the action of laughing.
Ich kann diesen Witz nicht hören, ohne zu lachen.
I cannot hear this joke without laughing.
The verb 'lacht' is the present tense conjugation for 'lachen' with the pronoun 'er' (he). This shows a habitual action.
Er lacht immer laut über meine Geschichten.
He always laughs loudly about my stories.
The verb 'gelacht' is the past participle form of 'lachen', used with 'haben' to form the perfect tense, describing a completed action.