What is the meaning of concretion?

noun

• The formation of stonelike objects within a body organ (e. G., the kidneys. )
• A hard lump produced by the concretion of mineral salts; found in hollow organs or ducts of the body.
  • usage: "renal calculi can be very painful"
  • synonyms: calculus
• An increase in the density of something.
  • synonyms: compaction, compression, densification
• The union of diverse things into one body or form or group; the growing together of parts.
  • synonyms: coalescence, coalescency, coalition, conglutination