ClearAll

ClearAll[s1, s2, ...] clears all definitions associated with the symbols.

Attributes[ClearAll] := {HoldAll, Protected}

Simple examples

In[1]:= Attributes[mytestsym] = {HoldAll}
Out[1]= {HoldAll}

In[2]:= mytestsym[5] := 6
Out[2]= Null

In[3]:= mytestsym[7] := 8
Out[3]= Null

In[4]:= Length[Attributes[mytestsym]]
Out[4]= 1

In[5]:= Length[DownValues[mytestsym]]
Out[5]= 2

In[6]:= ClearAll[mytestsym]
Out[6]= Null

In[7]:= Length[Attributes[mytestsym]]
Out[7]= 0

In[8]:= Length[DownValues[mytestsym]]
Out[8]= 0