proxy port

I am trying to buy residential proxies and it says they charge a monthly fee (which I am fine with)
but also they charge $12 a month "per port"
I don't know what "port" means. How many ports will I need? Ideally, I want like 50 residential IPs

@BassTrackerBoats can we get this moved to proxy section
https://www.blackhatworld.com/forums/proxies.101/

Proxies mean IP: Port,
Residential IP proxies are the back connect proxies, that need a gateway server to rotate the IPs,
You just need to connect to gateway proxy server, IP/HOSTort, then the proxy provider helps you rotate their IP automatically.

Their IP pool(proxies) are allotted to a different port, So more port means more IPs, also some proxy provider has limited the threads (Use Same/different proxies on the same time), so more ports mean more threads also.

So, if you want to get 50 residential IPs not the same time, easily buy one port will be fine, if you need to use 50 IPs at the same time you need to check how many threads allowed.