What is matched filter in QPSK signal?
Well, you're not going to send and receive those symbols directly, you know?

What you'll need to convey the information over a channel is a waveform. Your receiver will then typically use the same waveform to correlate the signal. Say you are using root raised cosine pulses to transmit, then your receiver will employ a root raised cosine filter as a pulse matched filter to maximize the SNR.

There may be other things you can matched filter against. For instance, if you have an idea what your channel looks like, you might use a channel matched filter to maximize the SNR conveyed over your channel. Or maybe you are using spread spectrum techniques to transmit your information or things like code multiplex? You might want to use a code matched filter.

So, matched filtering can be used for a lot of things, the term alone doesn't tell it...