A fractional CIO is an individual who has the credentials and expertise to act as a CIO but does so on a part-time basis for multiple clients at one time.
Basically, a fractional CIO is an outsourced CIO. A fractional CIO may also be referred to as a virtual CIO (vCIO).
Outsourcing a CIO's responsibilities should not a foreign concept. Many business owners are familiar with fractional CFOs—the same logic applies to this field.