The answer depends on the context. It might be the .NET Common Type System.
In serial communications, it stands for Clear To Send -- a hardware
handshaking line that signals from the connected device that that device is
prepared to accept data.
There may be other less common meanings for CTS.
Richard Grier, MVP
Hard & Software
Author of Visual Basic Programmer's Guide to Serial Communications, Fourth
ISBN 1-890422-28-2 (391 pages, includes CD-ROM). July 2004, Revised March
for details and contact information.