The following words are all reserved for internal functions in Lua.

• and, 
• break, 
• do, 
• else, 
• elseif, 
• end, 
• false, 
• for, 
• function, 
• if, 
• in, 
• local, 
• nil, 
• not, 
• or, 
• repeat, 
• return, 
• pairs,
• then,
• true, 
• until, 
• while

These words cannot be used for variable names, but Lua is case sensitive, so 'and' is reserved and can't be a variable, but 'aND, aNd, AND, anD, AnD, And, ANd' are not reserved and can be used as variables.