Flex (short for Flexible Box) is a layout mode in CSS that arranges elements within a container so that they can be laid out in any direction (left to right, right to left, top to bottom, or bottom to top) and can have flexible sizes. It is designed to give more control over how elements are laid out and makes it easier to create complex and responsive layouts.
Grid is another layout mode in CSS that allows you to create a grid of rows and columns, and place elements within the grid. It is more suited for creating layouts that have a fixed number of rows and columns and is often used for creating layouts that are more grid-like in nature.
One key difference between Flex and Grid is that Flex is more suited for one-dimensional layouts, where elements are laid out either in a row or a column, while Grid is better suited for two-dimensional layouts, where elements are laid out in a grid of rows and columns. Flex is also more flexible and easier to use, while Grid requires more planning and is more rigid in its layout.