In WordPress, post formats is a way to choose different ways in order to display the content in a post according to preset variables. Post formats are a function of your theme, so keep in mind that the post format options available to you depend on your theme.
Note: Unlike many other things in WordPress, however, you cannot create a custom post format, only use one or more of the built-in post formats, which are:
Standard – The default post format option.
Aside – Used for shorter posts to quickly share some information. Posts that are classified as asides often do not contain a title.
Gallery – Two or more images grouped together in a gallery.
Link – Contains a link to a different website or to other content previously published on your website.
Image – Contains a single digital photograph or other type of image.
Quote – Used to display a quote.
Status – Similar to social media sites like Twitter or Facebook, this is a short line of text to update your users about what you are currently doing or thinking about.
Video – Contains a video file playable inside the post.
Audio – Contains a sound file.
Chat – A transcript of a conversation or chat.
The way that each of the post formats is displayed (including size, color, formatting, etc.) to a visitor depends on your theme. Depending on which theme you are using, you may be able to customize how each post format is displayed.
The standard post format is the one you should use if you are creating longer posts or posts with a combination of different elements (like images, links, and videos). Use the other post formats for shorter posts with just one element.