Kahulugan ng buhay is a fairly common phrase which is generally taken to mean the meaning of life. However, it can be alternatively parsed without commission of grammatical errors to signify the meaning of the word "life". This would similarly be the case in the English sentence What is the meaning of life?, that is, either a query about the definition of the word "life" or a philosophical cogitation as to the significance of existence itself.
To avoid any misapprehension, use Kahulugan ng buhay if you mean to say the meaning of life and use Kahulugan ng salitang buhay if you mean to say the meaning of the word life.