pronoun
everything, all
A1
Means 'everything' or 'all' (neuter singular indefinite pronoun). Used to refer to all things collectively. Indeclinable in many uses (alles in nom/acc/gen/dat), contrasted with 'alle' for plural persons/things. Common in phrases like 'alles Gute' or 'alles ist in Ordnung'. Also used in questions.
Examples
Ich habe alles gekauft, was auf der Liste stand.
I bought everything that was on the list.
Alles ist bereit für die Party.
All is ready for the party.
Die Schüler fanden alles, was der Lehrer sagte, wichtig, obwohl sie müde waren.
The students found everything that the teacher said important, although they were tired.
Details
Mnemonics
picture a box labelled 'alles' containing everything
sounds like English 'alls' (all things)
Notes
'alles' is an indefinite pronoun that is neuter in form and often used as a nominal phrase.