toki pona taso (initialism: tpt) is a phrase meaning "Toki Pona only". If a community or open resource has this label, contributions should not be in any other languages than Toki Pona. There are many toki pona taso spaces that can be used for immersion and by proficient speakers. For a list, see Communities § toki pona taso.
The word kokosila is an antonym of this phrase. It means "to speak a language other than Toki Pona in an environment where Toki Pona is more appropriate". The command o kokosila ala! can be substituted for o toki pona taso!