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Definition of DL. 1  DL is short for down-low, which basically means to keep things under-wraps, to keep a secret or lay low. 2  I'll tell you this, but, you gotta promise to keep it on the DL. D.L. means down low. it means that something is not known to all. if you keep something on the D.L... 2  you don't share it with others. 3  I don't want my Dad to find out, so keep it on the D.L. 4  She like me but keep that on the DL.
What is a DL? DL stands for dimension lengthwise and is a common size for envelopes and promotional materials such as brochures and flyers. The C Series in the ISO 269 standard defines DL size to be 100mm Ã 210mm, which is also exactly a third the size of an A4. Usually DL size stock will be used for envelopes, brochures, flyers, leaflets, cards and invitations. In the ISO paper size system, the height-to-width ratio of all pages is the square root of two. In other words, the width and the height of a page relate to each other like the side and the diagonal of a square.