cutting edge

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An effective quality or element.
• noun The position of greatest advancement or importance; the forefront.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun the sharp edge of the blade of a knife or other cutting tool
• noun idiomatic (by extension) the forefront, or position of greatest advancement in some field
• adjective Alternative form of cutting-edge.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the position of greatest importance or advancement; the leading position in any movement or field
• noun the sharp cutting side of the blade of a knife