Accordion pleats are mini knife pleats and they are usually no more than ½” wide. If you want to get even teenier, there are Crystal pleats that sit around 1/8” wide. These fiddly kinds of pleats are often made by professional pleaters and heat-treated to keep their shape.
The knife pleat is considered to be the most basic pleat. You create a fold in the fabric at a predetermined width, and press in one direction on the right side of the fabric. Unlike other types of pleats, knife pleats always travel in a gang. Just one or two would be considered more a tuck than a pleat. Because you are working in multiples, you need to mark your fabric very accurately.