Maqams are named often after the region from which they came, some are specific to their local area and others are hybrids mixing Arabic with Turkish or Persian.
So, what are maqams exactly?
A maqam is not a scale in the Western sense. Maqam is a set of notes with traditions that define relationships between them, habitual patterns, and their melodic development. The closest equivalent in Western music is the mode (e.g. Major, Minor, etc.) Another way of defining the concept of a maqam is that it is a melody around a specific scale pattern. Arabic music is then the accumulated body of such recognized scale patterns or groupings.
Arabic scales are not eventempered like the Western chromatic scale. Instead, 5th notes are tuned based on the 3rd harmonic. The tuning of the remaining notes depends entirely on the maqam. So, the same note may have a slightly different pitch depending on which maqam it is played in.
The variations in pitch are broken down to quarter tones, falling approximately halfway between two semitones. These quarter tones are rarely precise and include microtonal subtleties depending on the maqam in which they are used. So, when writing Arabic music using Western notation, there is an understanding that the exact tuning of each note might vary with each maqam and must be learned by ear.
The building blocks of a maqam are sets of 3, 4, or 5 notes, called trichords, tetrachords, and pentachords. The Arabic word for these sets is jins (Engl. = gender, type). In general a maqam is made up of a lower and an upper jins, which can be joined at the same note, two adjacent notes, or overlap each other.
A maqam can also include other secondary ajnas, which are very useful for modulation. So, rather than thinking of a maqam as a collection of 8 notes or more, it is more useful to think of it as a group of 2 or more sets or ajnas.
Each maqam includes rules that define its melodic development (or sayr) with a starting, ending and dominant note. The dominant note is the starting note of the second jins (often the 5th note, but sometimes the 4th or 3rd). The dominant note serves as the pivot note during modulation.
These rules let the player know which notes should be emphasized, how often, and in what order. 2 maqamat that have the same tonal intervals but where one is a transposed version of the other may be played differently.
Each maqam has a different character, which conveys a mood, in a similar manner to the mood in a Major or Minor scale, although that mood is subjective. Since classical Arabic music is mostly melodic (excludes harmony), the choice of maqam greatly affects the mood of the piece.