What does Mbps mean?
Mbps is the amount of bandwidth you can transfer data at over your ISP's network. Think of it as lanes on a highway, the higher mbps (lanes) you have, the more data (cars) that can move on it at the same time without having to wait.
Mbps vs MBps
Also, data transfer over a network is measured in megaBITS, where data stored on disk is measured in megaBYTES. Mbps (lowercase 'b' = bits, uppercase 'B' = bytes). This can seem confusing but all it means is that there are 8 bits in every byte.
500/500mbps (megaBits per second) has a maximum transfer speed of approx 62.5 megaBytes in each direction. (500/8 = 62.5).
Maximum Number of Connections
Regarding your question of maximum number of connections, this plays no role in it. You can have virtually unlimited connections, depending on what your workstation can handle. If having too many browser tabs open is slowing your computer down, it is more likely your computer is out of free memory (RAM).
A TCP connection is just state locally held by your PC and the remote side (ignoring stateful NAT along the way). It simply doesn’t exist “on the network”. As such, it has no relation to bandwidth whatsoever. – Daniel B – 2016-01-02T18:07:11.663
The two numbers refer to the maximum download and upload data rates. The numbers are listed separately because many ISPs offer different maximum rates for download vs. upload. The numbers have nothing to do with browser instances. – fixer1234 – 2016-01-02T18:15:05.637
1You can open as many connections as your hardware allows. – Ramhound – 2016-01-02T18:19:28.517