The Wolfram Language allows arbitrary hierarchical namespaces. However, several standard "contexts" are conventionally used for predefined purposes.

System` — the context for system-defined symbols

Global` — the default context for user-defined symbols

package` — the conventional context for public symbols in a package

package`Private` — the conventional context for private symbols in a package

$CellContext` — placeholder for the context of a symbol inside Dynamic

Cell$n`, Notebook$n` — unique contexts generated for cells or notebooks

Developer` — built-in symbols intended for advanced package development

Experimental` — symbols introduced in a particular version for experimental purposes