Web browsers take cares of laying a foundation for a webpage--though a lot of the times we tend to normalize/reset the CSS styles due to inconsistencies among the palettes default to different browsers. Some elements are default to be arranged in certain manners: Very often we see <div> occupying a whole block by itself, nothing else sharing a same row. Some other times we find text flowing and wrapping at the end of lines, inline with photos.
So far we have seen block and inline. While all elements are default to display: inline in XML, meaning that the contents run in lines unless breaking at line ends. HTML 5 defines some of the many basic properties, and browsers each deploy their default looks, for instance WebKit/Chrome. Though at times some inline elements may have widths and heights (an example being the replaced element <img>), generally all inline elements cannot have their dimensions set; their sizes are calculated based on the fonts (family, size etc.)--technically speaking, replaced elements like <img> can behave differently from non-replaced elements, and replaced elements may not necessarily follow width and height settings.
There are a lot more than block, inline and none for displaying elements.
To be more precise with the language and to explore the full tailoring of content arrangement, some keywords are designed to describe where the elements sit in a flow layout, and some are designed to describe a context in which the child elements should be arranged.
For example, block and inline (default) are display-outside values setting whether the element should start a new chunk, or continue to run in a same line (can be broken into multiple lines too). Note that these display-outside values are more meaningful in a flow layout context (see in the next paragraph).
Additionally, flow (default), flex, grid are display-inside values that decide the layout context for the contained elements. flow layout is generic and the child elements with block and inline display-outside values can alter the flow of the content, but flow is not the only layout context available out there.
With these two types of values, we can combine them to make display: block flow (experimental, doesn't yet work). However, usually we just say display: block and the display-inside will be default to flow. Alternatively, if we want display: block flex, using display: flex will have block by default nearly at all times.
Now what about none? It goes in a display-box category and nothing in the element nor the element itself will be considered in the page rendering.
For more display values, check out the references.