Indie/Independent is a broad term with many meanings, If refers to record labels, ways of doing business, styles of music and number of philosophies, For chart purposes, "Indie" labels were traditionally classified as such if their product was handled by a non-major distributor; for the purposes of the independent chart launched in 2009 a title is eligible "if it is released on a label which is 50% or more owned by an independent (or non-major ) Company. Irrespective of the distribution channel through which it is shipped or delivered.
So in other words when you are called an Indie Artist, you are an artist without a label.