What exactly is a TX collision in a context of a VM?

I'm inspecting a problem with a MongoDB replica set reelecting a primary multiple times per minute. It seems that there is something wrong with the network configuration, but I can't nail it down yet.

When running ifconfig on the virtual machine of one of the nodes, I see a high number of TX collisions on eth0:

RX packets 850479  bytes 253445128 (241.7 MiB)
RX errors 0  dropped 12070  overruns 0  frame 0
TX packets 512851  bytes 210486965 (200.7 MiB)
TX errors 0  dropped 0 overruns 0  carrier 0  collisions 2648104

I don't understand what it means.

When I search what exactly are TX collisions, all I find is that those are related to the actual, physical network cables. However, the hardware server hosting this virtual machine reports zero collisions.

So what exactly is a TX collision in a context of a virtual machine (a Debian 9 running on QEMU/KVM, hosted on Ubuntu 18, if it matters)?