highest <- geo$name[ head(order(geo$lat, decreasing=TRUE), n=10) ]

All examples of:

A. The name of a variable to store a value to.

highest, because it is to the left of <-.

B. The name of a variable to retrieve the value from.

geo, in two places.

C. The name of a column to get from a data frame.

name and lat, because they are to the right of $.

D. The name of a function to call.

head and order, because they are to the left of (.

E. The name of an argument to a function call.

decreasing and n, because they are to the left of = within the brackets of a function call.