A polycrystal is a material that is made of many smaller crystallites with varying orientation. The variation in direction can be random (called random texture) or directed, possibly due to growth and processing conditions. Fiber texture is an example of the latter.
Polycrystalline is a structure of a solid, such as brass, that when cooled form liquid crystals formed from different points within it. This creates many crystals within a structure, where these crystals meet is known as a grain boundary.