The dimension of the decay constant depends on the context in which it is being used. In general, the decay constant is a measure of how quickly a quantity or a system undergoes exponential decay over time.
In radioactive decay, which is a common context where the term "decay constant" is used, the decay constant (denoted by the symbol λ) has units of inverse time, typically per second (s^-1), per year (yr^-1), or some other unit of time^-1.
For example, if the decay constant of a radioactive substance is given as 0.05 s^-1, it means that on average, 0.05 atoms of the substance decay per second per initial number of atoms.
It's important to note that the specific dimensions of the decay constant can vary depending on the particular equation or system being described. It's always a good practice to check the context or formula where the decay constant is used to determine its exact dimension.