General Definition
It depends on the context.
It generally means: to avoid or neglect (a duty or responsibility). -- i.e. He shirked his duty to provide me the documents on time. (He failed to do his duty...)
However, in the case of Islam, shirk means: to bring [other deities] into partnership to Allah. -- i.e. to blaspheme, to apostasize, to be a polytheist or atheist.
Further to the Islamic Definition
Shirk means attributing partners to Allahu ta'ala. A person who does the attributing is called a mushrik(polytheist). There are kinds of disbelief. The worst, the gravest kind is shirk. It has been a generally accepted rule that when several subjects are to be referred to under one common nomenclature, the gravest one is mentioned. For this reason, the word shirk used in Qur'anic verses and hadith-i sharifs comprehends all sorts of disbelief.
The Qur'an al-karim says (what means):
(Allahu ta'ala never forgives shirk[all sorts of disbelief]. He forgives [all] sins [venial or grave] except shirk if He wills.) [An-Nisa' 48]
Shirk - to give a cold shoulder to, to ignore, to shine on.
It means to avoid doing your duties
Gary Shirk's birth name is Gary Lee Shirk.
Kasey Shirk's birth name is Kasey M Shirk.
Matthew Shirk was born in 1973.
Gary Shirk is 6' 1".
Kasey Shirk is 5' 5".
Stacy Shirk is 5' 5".
James Shirk died in 1873.
James Shirk was born in 1832.
Why do you continue to shirk your responsibility on the loading dock?
Adam Shirk was born in c. 1887.