Humanist Magazine has defined humanism as "a rational philosophy informed by science, inspired by art, and motivated by compassion. Affirming the dignity of each human being, it supports the maximization of individual liberty and opportunity consonant with social and planetary responsibility. It advocates the extension of participatory democracy and the expansion of the open society, standing for human rights and social justice." 
The above meaning is implied in common use, and is differentiated from definitions of humanism having other philosophical and historical meanings. WordNet 3.6 lists the following definitions of humanist:
1. (adj.) humanist marked by humanistic values and devotion to human welfare "a humane physician","released the prisoner for humanitarian reasons","respect and humanistic regard for all members of our species"
2. (adj.) humanist pertaining to or concerned with the humanities "humanistic studies","a humane education"6. (n.) humanist an advocate of the principles of humanism; someone concerned with the interests and welfare of humans 
3. (adj.) humanist of or pertaining to Renaissance humanism "the humanistic revival of learning"
4. (adj.) humanist of or pertaining to a philosophy asserting human dignity and man's capacity for fulfillment through reason and scientific method and often rejecting religion "the humanist belief in continuous emergent evolution"- Wendell Thomas"
5. (n.) humanist a classical scholar or student of the liberal arts
The definition of humanism ascribed to by A Voice for Men is the common version mentioned at top.