The constructor is ambiguous

The problem exists when you try to instantiate a class that could apply to more than one constructor.

For example:

public Example(String name) { = name;

public Example(SomeOther other) {
this.other = other;

If you call the constructor with a String object, there's one definite constructor. However, if you instantiate new Example(null) then it could apply to either and is therefore ambiguous.

The same can apply to methods with similar signatures.