Accumulations of weakly bound particles or aggregates or of compounds of these, whose resulting surfaces are similar to the sum of surfaces of the individual components. Agglomerates are held together by weak forces, for example Van der Waals forces or simple physical hooks. Agglomerates are referred to as secondary particles, while the unbound particles are known as primary particles.
See also ISO/TS 27687:2008 (E), International Organization for Standardization.