Voltage divider circuit load resistance?
Infinite resistance means no current, which means it can be ignored. Its a really good trick for analyzing circuits because it can make estimation much faster (and also a trick for opamp circuits).
If the load hand no resistance (0Ω) then all of the current would be diverted through the load and none through R2
A good exercise is to find the voltage for the no load (ideal) condition, then do it with a small load.
What one will find is a load pull down the divider, so a resistor divider doesn't do well with a load if voltage maintenance is the  goal