FB = Facebook :)
XDP = eXpress Data Path, it's an eBPF program that runs before the kernel network stack and allows you to process raw packets as fast as your network card will allow.
eBPF = extended Berkley Packet Filter is a BPF program that is compiled and run on a virtual machine in the kernel (allows you to run kernel code from userspace). It can talk to user space through maps and hook in to various parts of the kernel. An important point is that once compiled, an eBPF program is guaranteed to halt and has other verification performed on it, to make it safe to run in the kernel.
BCC = BPF Compiler Collection, is a set of tools for working with eBPF, it uses llvm and clang to make it easy to write eBPF programs in Python, Rust, etc.
butterFS = btrfs, the filesystem. People often call it butterFS in conversation, even though the btr stands for b-tree.
cgroups = Technically the work is on cgroup2, which changes the way processes are laid out in a resource hierarchy from the original cgroups. This is how resource constraints are placed on containers, although many people use it just to monitor processes (without constraining resources).