Flexbox is a layout module that is used to create responsive and flexible web page layouts. It is a one-dimensional layout, meaning it lays out elements in a single row or column. It is best used for small-scale layouts where elements need to be aligned and distributed within a container, such as creating flexible navigation bars, grids with equally-sized elements, and simple responsive design. Grid, on the other hand, is a layout module that is used to create responsive and flexible web page layouts.

Semantic tags are HTML tags that provide additional meaning and context to the content they enclose. They are used to describe the type of content contained within an HTML element, allowing browsers and search engines to understand the structure and purpose of that content.

Using semantic tags can make your HTML code more readable and understandable for both browsers and developers. It also helps search engines and assistive technologies to better understand the content of a web page, making it more accessible for users.