Conclusion: single-player can be played offline
Mojang's official explanation describes Minecraft single-player as playing offline and alone, while multiplayer is played online. This explanation covers both Java Edition and Bedrock Edition.
What you can do in single-player
Single-player can be played offline, making it an option during an internet outage or when no connection is available. This does not remove account requirements set by the device or platform you use.
Multiplayer and Realms
Online multiplayer, multiplayer servers, Realms and other features that connect you to players or online services require an internet connection. They are not available while offline.
Java Edition and Bedrock Edition
For both Java Edition and Bedrock Edition, the official distinction is the same: single-player is offline and multiplayer is online. The edition does not change that basic difference.
Microsoft Account requirements are separate from offline play
On Windows PC, a Microsoft Account is required for both Java Edition and Bedrock Edition. On Linux and macOS, Java Edition requires a Microsoft Account. Consoles and mobile devices also have account requirements set by their platforms. Requiring an account is not the same as requiring a continuous internet connection while playing.
What to check before travel or an outage
Account conditions vary by device and platform. Before you expect to be offline for a long time, confirm that the game is usable on the device you will take and complete any necessary account steps or updates while you still have a connection. This page does not assume specific launcher behavior that has not been confirmed here.
Free trial
The official Minecraft free trial can also be played offline. Online multiplayer servers are not available in the trial while offline.
Frequently asked questions
Can I use Realms offline?
No. Realms requires an internet connection.
Do both Java and Bedrock support offline play?
Yes. Single-player in both editions is described as playable offline; multiplayer is online.
If I need a Microsoft Account, do I also need to stay online?
Those are separate requirements. An account requirement does not by itself mean continuous connectivity, but you should still check the conditions for your device and platform before relying on offline play.