Just a slight gloss. To see if something is an object, use
ls()
which will return a list of all objects in the workspace.
R also knows about other objects, such as packages that have been installed and the data objects in them, such as the famous data(iris) dataset.
Otherwise, a string, such as "LAX" can be assigned to an object or given as an argument to a function.
origin <- "LAX"
install.packages("dplyr")
and that's the long-winded explanation of @pete's advice to enclose the string in quotes when you see that message.