There is an important grammatical difference: 'Laugh' is a countable noun. 'We had some laughs' 'She has a loud laugh'. Ben has given you some good definitions of the use of 'laugh' as a noun, usually in the singular, occasionally in the plural/ I'd just add the idiomatic phrase 'to have laugh' , which means to have fun or find something amusing eg 'We had a laugh when we heard about John's silly mistake.' 'Laughter' is an uncountable noun, which means that it can't go with the indefinite article and has no plural form. 'Laughter' is a more abstract concept than 'a laugh', and refers to the physical ability or human capacity. For example 'Laughter is the best medicine'. The best things in life are health, love and the sound of laughter. I hope that helps.

Laughter can only be used as a noun, means ' the sound of people laughing' while laugh can be used as a verb or a noun. Mostly it used as a verb e.g ; you made me laugh (verb)

If both used as a noun, laugh (most of the time) has a negative connotation while laughter is a result of amusement and has some positive impact to the listener. Otherwise, to laugh is a verb, laughter is a noun.

Yes. "Laugh" has only one syllable; "laughter" has two.

"Laughter" - noun - is an uncountable noun meaning the action or sound of laughter. Example: Our summer holiday was full of laughter. Laugh - noun - means: 1. a single act of laughing. Example: He let out a loud hearty laugh. 2. a characteristic way of giving a laugh. Example: He has a squeaky soprano laugh. 3. something or someone that causes laughter, or is a source of derision. Example: That political party broadcast was a laugh.