The Difference between lead screws and ACME screws?

Lead Screws

The term "Lead screw" refers to any threaded drive screw that utilizes sliding surfaces to transmit a load.

ACME Screws

The term "ACME" refers to a particular thread form. Specifically an ACME thread form is one with a 29 degree included angle.  All ACME screws are in the parent category of lead screws and not all lead screws are ACME screws. The ACME thread form standard includes several classes such as 2G, 3G and 2C which have slightly different tolerances.  ACME thread forms are easily checked using available thread gauges.  The ACME thread standard is designed for interchangeability and its ease of manufacture.

Various Other kinds of Screws

Fasteners use a "V" type thread form and are generally referred to as  locking screws.  These types of screws utilize inefficient thread forms to allow the screw and nut to lock under load and prevent the nut from back-driving These types of thread forms  and fasteners are not well suited for regular motion.