If the clients roam between APs registered to different controllers and the client WLAN on the two controllers is on different subnet, then it is called inter-controller L3 roam.
In this situation as well controllers exchange mobility messages. Client database entry change is completely different that to L2 roam(instead of move, it will copy). In this situation the original controller marks the client entry as "Anchor" where as new controller marks the client entry as
"Foreign".The two controllers now referred to as "Anchor controller" & "Foreign Controller" respectively. Client will keep the original IP address & that is the real advantage.
Note: Inter-Controller (normally layer 2) roaming occurs when a client roam between two APs registered to two different controllers, where each controller has an interface in the client subnet.

A fabric edge node provides onboarding and mobility services for wired users and devices (including fabric-enabled WLCs and APs) connected to the fabric. It is a LISP tunnel router (xTR) that also provides the anycast gateway, endpoint authentication, and assignment to overlay host pools (static or DHCP), as well as group-based policy enforcement (for traffic to fabric endpoints).
From Cisco's guide, under SDA roaming - When a client on a fabric enabled WLAN, roams from an access point to another access point on a different access-switch, it is called Inter-xTR, like a highway. Intra is within intra is between. Like interstate highways. That's how I remember.
https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/config-guide/b_wl_16_10_cg/mobility.html