Files having extension .BMP represent Bitmap Image files that are used to store bitmap digital images. These images are independent of graphics adapter and are also called device independent bitmap (DIB) file format. This independency serves the purpose of opening the file on multiple platforms such as Microsoft Windows and Mac. The BMP file format can store data as two-dimensional digital images in both monochrome as well as color format with various colour depths.
PSD, Photoshop Document, represents Adobe Photoshop's native file format used for graphics designing and development. PSD files may include image layers, adjustment layers, layer masks, annotations, file information, keywords, and other Photoshop-specific elements. Photoshop files have default extension as PSD and have a maximum height and width of 30,000 pixels, and a length limit of two gigabytes.
You can also convert BMP into many other file formats. Please see the complete list below.