Intracellular

Not to be confused with intercellular, meaning "between cells".

In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".

It is used in contrast to extracellular (outside the cell). The cell membrane (and, in plants, the cell wall) is the barrier between the two, and chemical composition of intra- and extracellular milieu can be radically different. In most organisms, for example, a Na+/K+ ATPase maintains a hi potassium level inside cells while keeping sodium low, leading to chemical excitability. This terms also means existing within the cells.