Fortis (definition)
From Scottish Gaelic Grammar Wiki
these are types of sounds which are made with a lot of muscle movement and forced breath. These types of sounds are usually voiceless. The term tense, when used in reference tense vs.lax, means the same thing as well. In English “p”, “t”, “f”, and “s” are some examples of fortis consonants.
See Also
External Links
http://en.wikipedia.org/wiki/Fortis_and_lenis
http://www.statemaster.com/encyclopedia/Fortis-and-lenis
http://wapedia.mobi/en/Fortis_and_lenis
References
Crystal, David (2008). A Dictionary of Linguistics and Phonetics Sixth Edition. Blackwell Publishing Ltd.
Crystal, David. A Dictionary of Linguistics and Phonetics. The language library. Oxford, UK: Blackwell, 1997.