A nanosecond (ns) is a unit of time in the International System of Units (SI) equal to one billionth of a second, that is, 1/1000000000 of a second, or 10 seconds.
The term combines the SI prefix nano- indicating a 1 billionth submultiple of an SI unit (e.g. nanogram, nanometre, etc.) and second, the primary unit of time in the SI.
The erg is a unit of energy equal to 10 joules (100 nJ). It is not an SI unit, instead originating from the centimetre–gram–second system of units (CGS). Its name is derived from ergon (ἔργον), a Greek word meaning 'work' or 'task'.
An erg is the amount of work done by a force of one dyne exerted for a distance of one centimetre. In the CGS base units, it is equal to one gram centimetre-squared per second-squared (g⋅cm/s). It is thus equal to 10 joules or 100 nanojoules (nJ) in SI units.