If you are seriously asking, why don't you go back to the post earlier in the thread where I linked the Strong's concordance for you? I gave you several resources to help you truly understand
Common is basically the opposite of holy, or set-apart.
Our clothing that we wear is common, it's not set-apart. Aaron and the priests had set-apart/holy garments, which is the opposite of common. Set-apart means exactly what it says. It's set-apart for special use. It's consecrated. It's holy/set-apart.
When Aaron and the priests would take off their set-apart/holy garments, they would put on what you could consider "common" clothing.
They had a tradition in Peter's day, where they would not eat clean animals that had been around unclean animals. That was not a sin according to the law. They were rejecting what God had cleaned(the clean animals), and were calling it unclean. Peter did this during the vision. He called the clean animals common & unclean.
They considered clean animals that had been around unclean animals "common", and that they were not fit for consumption, but that was not true - that's not according to the law of God. Their tradition was that the clean animal that they considered "common" was also unclean. Not so. Remember, God only cleaned certain animals. These were the beasts Peter could have eaten, but he rejected all of them. It was okay to eat the clean animals, even though they had been touching the unclean.
The law says we can eat clean animals - it doesn't say that we can't eat clean animals if they've been around unclean animals. The tradition in Peter's day was that they refused clean animals(because they had been around unclean animals), which was WRONG, you shouldn't refuse clean animals, just like Peter shouldn't have been rejecting the Gentiles who were coming to faith. Obviously Peter would not be accepting and hanging out with people who don't believe and reject Messiah. He would be accepting Gentile Believers of Messiah.
This is what Peter's vision is all about. God is correcting him on his understanding of accepting Gentiles, by teaching him that first, it is acceptable to eat clean animals that had been around unclean animals. And that Peter should also accept the cleaned gentiles, which represent cleaned animals on the sheet, just like he should eat the clean meat that was around the unclean.
Peter was not accepting believing Gentiles(a clean animal) that had come out from around the unbelieving gentiles(unclean animals).
Hope this helps
ETA: the word used for common in Peter's vision is (koinos), which is the same word Paul used in Roman's 14:14 all 3 times: common. Not the word as unclean(akathartos)
