LECA stands for "light-weight expanded clay aggregate," and these round, little balls are used for soilless plant care and growth. 

LECA is most often used for hydroponic plant care to cultivate a plant in a container with water, but no soil. Extra nutrients to feed the plant are needed with this technique, as there is no organic material from soil used with hydroponic plant care.  A water soluble fertilizer is recommended to help the plant thrive long term. 

LECA can also be used as a drainage layer to a potting soil mix, or added to a soil mix to increase drainage.  

It's recommended to rinse LECA very well before using to remove any excess salts from the manufacturing process.