These words turn up in every relaxed conversation. All of them are spoken, informal Finnish:

Spoken	Neutral Finnish	English
siisti / makee	hieno	cool, great
kaveri	ystävä	mate, friend
juttu	asia	thing, matter
tosi	todella, hyvin	really (tosi hyvä — really good)
meininki	tunnelma	vibe, what's going on
hengailla	viettää aikaa	to hang out
bileet / bilettää	juhlat / juhlia	party / to party
moikka / heippa	hei / näkemiin	hi / bye

Siisti also means tidy in written Finnish — siisti huone is a tidy room. In casual speech, Siistiä! is simply Cool!