Translation guide
In Japanese, 'online game' is commonly expressed using the loanword オンラインゲーム. This is the most natural and widely understood term. Other expressions exist but are less common or more specific.
online game
Referring to any game played over the internet, including PC, console, and mobile games.
The standard katakana loanword for 'online game'. Used in all contexts.
I recently started a new online game.
I like playing online games with friends.
A common abbreviation of インターネットゲーム. Slightly more casual than オンラインゲーム.
I'm hooked on online games.
Slang abbreviation of ネットゲーム. Used mainly in online communities and by gamers.
I'm going to pull an all-nighter playing online games tonight.
Specifically a game played in a web browser, often without downloads.
Directly means 'browser game'. Used when emphasizing the platform.
You can play this browser game for free.
An online game played on a smartphone or tablet.
A large-scale online game with many simultaneous players.
The abbreviation MMO is widely understood among Japanese gamers.
He's an MMO addict.
Specifically a massively multiplayer online role-playing game.
This MMORPG is popular worldwide.
オンラインゲーム is the safest and most common term. ネットゲーム is slightly more casual but still widely used. ネトゲ is slang and should be avoided in formal settings.