Basically, philosophy as an area of study encompasses a number of important problems. For example, what we can know or how we know stuff, or how we should behave and judge the behaviour of others. Such things are foundational to all kinds of human endeavour and even our regular lives.

There's different ways we might go about dealing with such problems. We can try to ignore them, and maybe just rely on received wisdom or prevailing cultural attitudes. Or we might idly speculate and come up with answers that seem pleasant or particularly in accord with our intuitions. Or we might pray, meditate, take a lot of hallucinogenics, etc. and see if any answers reveal themselves to us. These might all work out fine for us if we're just looking to get on with life and not trouble ourselves with such matters, but they probably aren't satisfactory if we want to know what's actually true. So the alternative is philosophy as a discipline: attempting to work out these problems in a rigorous and critical way.

Usually when people are dismissive of philosophy it's because they either don't understand that rigor can be applied to these kinds of problems, or just think that philosophy isn't about doing that (e.g., that it's the "idle speculation" approach).