What is meant by drivers side drop and passenger side drop when it comes to a straight axle? New here and still learning thanks

It's a reference to what side the diff is on. If the diff is closer to the driver's side, it's a driver's side drop.

to take it a step further, the front output on the transfer case may be on the passenger side or the driver side. for instance, hilux trucks up to 95 have the output on the right (passenger), while tacomas (95.5 and newer) have the output output on the left (driver) side. you can mix and match drivetrain components to find something workable or save money. an example would be running an 85 solid front in a tacoma by changing the output from left to right.

But remember, some manufacturers move the engine over an inch or two to clear the front drive shaft. So there may be more work than just swapping transfer case out puts from one side to the other.