What the sign label means
The seventh 30° segment. A chart may contain no planets in Libra; that does not make the sign or its house disappear.
A body is listed in Libra when its normalized sidereal longitude falls from 180°00′ up to—but not including—210°00′. The exact degree within the sign remains important, particularly near either edge.
Sign is not the same as house
The sign is a fixed part of the 360° circle. In a whole-sign chart, the house number depends on the ascendant: the rising sign is house one, and the following signs are numbered in order. Libra can therefore be a different house in different birth charts.
Element and mode are traditional classification labels. They do not, on their own, establish a personality or predict an event.