The capacity for or the practice of recognizing and respecting the beliefs or practices of others.
It is about respect.
Traditional definition: "The word 'tolerance' simply means 'sympathy or indulgence for beliefs or practices differing from or conflicting with one's own.' By definition, to tolerate someone implies that you do not agree with his views, You're simply willing to indulge them."
It is not about agreeing, but recognizing.
Another way of saying it is "bearing or putting up with someone or something not especially liked".
However, today in the post modern culture, the word has been redefined to 'all values, all beliefs, all lifestyles, all truth claims are equal.' Once, tolerance was defined as recognizing and respecting others' beliefs and practices even without sharing them. Tolerance would often necessarily entail enduring, or putting up with, someone or something not especially liked.
But today's definition of tolerance is very different. Now, a "tolerant" person views all values, beliefs, lifestyles, and truth claims as equal. This language shift is eloquently described in Josh McDowell and Bob Hostetler's 1998 book, The New Tolerance.
Where this new tolerance reigns, there can be no hierarchy of truth, and no standard by which to discern between competing truth claims. Every man's position must be praised and considered equally valid. This is because the new tolerance considers all truth claims to be mere opinions--not absolutes that are true across time and cultures, but culturally created and culturally conditioned ideas.
By this new standard, any system of belief which claims to be transcendent and absolute--making truth claims that are not qualified as relative according to time, place, and person--is considered to be "intolerant." In a society which scorns absolutes and denies the existence of any natural law written on the heart, or any intrinsic human nature, there can be only one universal virtue--tolerance--and that virtue must be enforced with almost religious fervor. 
