This tag implies that the bands and artists are Serbian or originated in Serbia. Music represented by this tag is often highly commercial. Other, possibly better, Serbian tags are, for example Novi Val or nova srpska scena.
Relapse means that the teeth can take up to one year or more to stabilize after treatment. If you had gaps between your teeth before treatment, the retention period will be longer. Usually, retainers are worn for as long a time as you have had your braces.
The way the system works is you wear a set of Invisalign trays (called aligners) for two weeks at a time. Each tray is manufactured so that the teeth are slightly straighter than the previous tray. The teeth will typically move 1/10mm per tray.