Pencil pleat curtains feature tightly gathered fabric at the top which is held by a cord on the heading tape.  The pleats resemble a row of pencils, hence the name.  A pencil pleat finish is good for hiding the curtain rail with a more formal appearance.

Tab top curtains feature fabric loops that hang from the curtain rail.  The curtain rail is exposed, which results in a more contemporary look. Tab top curtains are most commonly made from lighter fabrics.

Eyelet curtains feature metal rings set into the top of the fabric, which a thin curtain rail can feed through.  The reinforcement of the eyelet allows heavier fabrics to be used than a tab top finish.  The gathering is typically not as formal as a pencil pleat curtain. 

Pocket curtains simply have a pocket sewn into the top through which the curtain rod feeds. This is a simple finish, best suited to lighter fabrics.