Click 

Press and release the left mouse button, without moving the mouse.  

Click-and-hold 

Press and do not release the left mouse button. 

Left-click 

Same as click. Left-click clarifies the action when there might be confusion with right-click.

Middle-click 

Press and release the middle mouse button, without moving the mouse.  

Right-click 

Press and release the right mouse button, without moving the mouse.  

Double-click 

Press and release the left mouse button twice in rapid succession without moving the mouse.  

Drag 

Click-and-hold a mouse button, then move an object. For example, you can drag a window or an icon. The left and middle mouse buttons can perform drag actions.  

Drag-and-drop 

Click-and-hold a mouse button, then move an object. For example, you can drag-and-drop a window or an icon. Release the mouse button to place the object in a new location.  

Grab 

Point to an item that you can move, and click-and-hold on the mouse button. For example, you can grab the titlebar of a window, then drag the window to a new location.