The word oma is usually classified as an adjective with pronoun-like properties. Here it is described as a pronoun of a special kind. It usually corresponds to “own” in English, but there are specialties in its use. It has regular inflection oma : oman etc.
Normally oma is used as an attribute, like an adjective, before a noun. The noun often has a possessive suffix in standard Finnish, e.g. Mies vastasi omalla tavallaan (The man responded in his own way). In expressions like Se on oma tarinansa (It is a story of its own), oma corresponds to “of its own” in English.
It is also possible to use oma in the role of a noun, mostly with a possessive suffix, e.g. Antaisitko kynän? Olen hukannut omani (Would you please give me a pen? I have lost mine). It may also mean one’s “own things” or “own people”, e.g. Älä ota toisen omaa (Don’t take what belongs to someone else; literally: “other’s own [thing]”).