Answer:
Liquid crystals are certain long chain organic chemicals that, although liquid they have a strong tendency to align in "crystal like" arrays. Normal liquids have no (or very little) order, liquid crystals have order approaching that of solid crystals.
Liquid crystals are useful in electronics (displays), temperature sensing (indicators), and other technologies because application of various stresses (e.g. electric field, heat) cause them to change their "crystal" properties in ways that solid crystals can't. These changes can then usually be made visible.