Save

Save["filename",symbol] appends definitions associated with the specified symbol to a file. 

Save["filename","patt"] appends definitions associated with all symbols whose names match the string pattern "patt". 

Save["filename","context`"] appends definitions associated with all symbols in the specified context. 

Save["filename",{object1,object2,…}] appends definitions associated with several objects. 

Please visit the official Wolfram Language Reference for more details and examples on core symbols.