Hard to tell by your post exactly what you're asking. According to you, your server room has a wireless router, which would make sense. This device is generating a wifi network (hotspot) at your place of business. This is, I assume, the network you sign on to. If you wander too far from the wireless router you can lose signal strength and lose the connection. Walls or ceilings built of certain materials (some beams contain lead) can also block or weaken RF strength. So you get kicked off, and have to sign back on.
Now there might also be other wifi networks generated in your area by other routers. Your network card has a software component that will show you all wireless networks it can detect in the area. It could be there is more than one at your place of business. Most NIC cards will automatically try to connect you to the network with the strongest signal strength. If this happens to be an encrypted network, it will ask you for a username and password before granting you access. If your NIC card is already configured with these credentials, it will supply them automatically and you'll get back on seamlessly.
Maybe all you are asking is if a "hotspot" is a public network only. It usually refers to a public wifi network, but can also be used to mean any wireless network, even within a business. It's just that most businesses encrypt their wifi networks to keep the public off of it, so that's not a very "hot" spot for public access. :)