A concept is the element of a proposition rather in the way that a word is the element of a sentence. Concepts are abstract in that they omit the differences of the things in their extension, treating them as if they were identical. Concepts are universal in that they apply equally to every thing in their extension.
Concepts are bearers of meaning as opposed to agents of meaning. A single concept can be expressed by any number of languages. The concept 'dog' can be expressed as 'Hund' in German, 'chien' in French, 'perro' in Spanish. The fact that concepts are in some sense language independent makes translation possible; words in various languages "mean the same" because they express one and the same concept.
The above usage of the word is quite modern, however. The definition below, (from Random House Unabridged Dictionary) is how the word was used up until not too many years ago:
1. a general notion or idea; conception. 2. an idea of something formed by mentally combining all its characteristics or particulars; a construct. 3. a directly conceived or intuited object of thought.
In popular music a concept album is an album which is pre-planned (conceived), most often with all songs contributing to a single overall theme or unified story, this plan or story being the concept.
Concept albums are especially common in the progressive rock genre of the 1970s, although rarely did that equal a lasting commercial or critical legacy for the band or artist involved.
This concept album was a sequel to their original song from their 1992 album Images and Words, about a present day man's nightmares of his death in his previous life in 1928.