what does "Renew !ease" mean in wifi settings?

This indicates that your iPad is configured to use DHCP (Dynamic Host Control Protocol) to obtain its network settings - this includes it’s local IP Address and Default Gateway IP Address (this, in most cases, is the Router that connects your local WiFi network to the internet).

When you use DHCP to configure your network settings, the DHCP Server (usually part a your WiFi Router) assigns your IP Address a “lease time” - during which time your device uses its assigned IP Address. When the lease-time expires, or if you manually “renew” your lease, your iPad will request a new IP Address to use (very often, you will be re-assigned the same IP Address).

For the most part, if using DHCP, your network addresses are automatically and transparently managed. Unless you have a more complicated network, requiring setup of DHCP, you can usually forget all about it.

This is intentionally a much simplified overview description. If you are interested in learning more about DHCP and networks, this page may be of interest:

https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol

It means that the modem-router which you're trying to connect your device to is using DHCP management system and your iPad's MAC address needs to be confirmed/renewed.

If this happens while connecting your device to your home wifi network, you need to change/manage DHCP settings on your modem-router.

If this happens on a different wifi network (different modem-router), you need to contact the IT admin/supervisor of that wifi network and ask them.

Regards

Giulio

How the DHCP Lease Renewal Process Works - Network Services Windows Server 2003 (serverbrain.org)

TL;DR you may get a new IP address