MTU
In plain terms
The largest packet size a network link can carry.
Going deeper
The Maximum Transmission Unit sets the biggest packet that can pass without fragmentation; mismatches cause performance issues. It bounds packet size per link.
Under the hood
Path MTU discovery avoids fragmentation; wrong MTU (e.g., over VPNs) causes drops and slowdowns.
Examples
Ethernet (1500 bytes), VPN tuning, jumbo frames, fragmentation issues.
Think of it like...
Like a tunnel's height limit, vehicles taller than it must be split or rerouted.