A few definitions for the word Blah as defined by the Urban Dictionary:
a word commonly used to describe an emotional state in which the person feels a sense of having no hope; usually during a deep depression.
1.A word that describes an unknown situation.
2.A word that describes an unknown feeling.
3.Used when you don’t know the answer to something.
a description of something so bland, drab and/or gray its neutrality has actually become undesirable.