Is a Rav’s Psak Just His Opinion Without Semicha?

Without formal semicha in the old Sanhedrin sense, is a modern rav’s halachic ruling just personal opinion one can disagree with?

Q. What does it mean that a rav gives his psak its not halacha since he doesn’t have semicha from the Sanhedrin so is it just his opinion and can one disagree?

The semicha that we have today allows a rav to give his psak, and his community follows it. That being said, in almost all questions, the psak has already been decided by the leading poskim, and all the local rav has to do is to quote them, and apply them according to the needs of the community and the individuals involved. When a truly new situation or case arises, he will generally refer it to the leading halachic authorities, informing them of the entire situation and the people involved.