字幕指以文本形式显示电视、电影、舞台作品里面的对话等非影像内容，也泛指影视作品后期加工的文本。

影视作品的对话字幕，一般出现在屏幕下方；而戏剧作品的字幕，则可能显示于舞台两旁或上方。

字幕与声音语言相比，声音语言有一定的局限性：有声无形，转瞬即逝，不易引起人们的注意，有时不易听懂。如人物的语言和戏词，有的因口音或语种的原因，受众便很难听清或听懂，加上字幕就可以弥补这种局限性。因此，字幕与声音和画面相比，具有独特的功能。

中国各地方言差异较大，给电视节目配上字幕，首先消除了语言隔膜，其次能够避免因为现场环境（噪声）和拾音器材的质量等客观因素而造成的传播障碍。又如播映《三国演义》《水浒传》时，演员念文言台词，加上字幕就便于观众理解。

Subtitles are derived from either a transcript or screenplay of the dialog or commentary in films, television programs, video games, and the like, usually displayed at the bottom of the screen, but can also be at the top of the screen if there is already text at the bottom of the screen. They can either be a form of written translation of a dialog in a foreign language, or a written rendering of the dialog in the same language, with or without added information to help viewers who are deaf and hard of hearing to follow the dialog, or people who cannot understand the spoken dialogue or who have accent recognition problems. The encoded method can either be pre-rendered with the video or separate as either a graphic or text to be rendered and overlaid by the receiver. The separate subtitles are used for DVD, Blu-ray and television teletext/Digital Video Broadcasting (DVB) subtitling or EIA-608 captioning, which are hidden unless requested by the viewer from a menu or remote controller key or by selecting the relevant page or service (e.g., p. 888 or CC1), always carry additional sound representations for deaf and hard of hearing viewers. Teletext subtitle language follows the original audio, except in multi-lingual countries where the broadcaster may provide subtitles in additional languages on other teletext pages. EIA-608 captions are similar, except that North American Spanish stations may provide captioning in Spanish on CC3. DVD and Blu-ray only differ in using run-length encoded graphics instead of text, as well as some HD DVB broadcasts.