Sheela na Gigs are stone carvings depicting a naked female exhibiting herself in an explicit and provocative way. These images are found throughout Ireland and in parts of England.  Theories abound as to their meaning and dating, with a consensus almost being arrived at which agrees that they appear mostly on churches and castles built after the 12th century and are possibly a continuation of a much earlier pagan custom. There are many opinions as to what the figures represent and their raison d'etre. These opinions are as diverse as the shapes and styles of the Sheelas themselves and include  Pagan Spirit, Mother Earth, Earth Goddess,  Pagan Goddess, good luck symbols, fertility symbols, figures to celebrate womanhood etc.  It is widely believed that they repel evil spirits. 

Meaning of Sheela na Gig
In spite of the very biased and inaccurate article on Wikipedia regarding the derivation of the name Sheela na Gig......the name is Irish and there is no consistent name for these carvings in the English language.  Some misguided people almost stand on their heads rather than acknowledge that the name is Irish.  The simple name is explained below.  It is worth noting, that the earliest mention of Sheela na Gig was at Drury Lane in 1780 when an Irish lilt named 'She La Na Gig' was performed.  

Interpreting Shee Lena Gig
Here is the real meaning of the name Sheela Na Gig.     It is a fact that placenames in Ireland are almost always corruptions of Gaelic words and one has to listen to the placename rather than read it in order to understand it.  It is necessary to hear the name as our ancestors heard it. One of the foremost authorities on placenames in Ireland is Joyce and anyone with an interest in Irish placenames should make an effort to get a copy of his book.  

So, following this logic of listening to names rather than reading them, a Gaelic speaker can hear the words 'Sheela na Gig' as being  - in Gaelic - Sidhe Lena Gig.  This is pronounced 'Shee Lena Gig'.  Sidhe is the Gaelic for Fairy Woman.  Lena is the Gaelic for 'with her' and Gig is the Gaelic for sexual appendage.  So....  Sheela na Gig is 'Sidhe Lena Gig' and means Fairy Woman with her sexual appendage.  

P.W. Joyce, the foremost scholar in Irish placenames has this to say on page 184, vol. 1, Irish Names of Places, 1901:

"Sidh  [pronounced Shee] as we have seen, was originally applied to a fairy palace and it was afterwards transferred to the hill, and ultimately to the fairies themselves; but this last transition must have begun at a very early period, for we find it expressly stated in the Leabhar na hUidhre [early 12th century] , that the ignorant call the fairies Side [plural].  At the present day, the word generally signifies a fairy..."
The name was probably used in its correct form for many hundreds of years in Ireland. 

Ard fuaim na n-uisgi éadtroma -- Shallow Waters make great Noise (Old Irish Proverb)