Here's what the controller bible says in the US about holding... There is a lot of other stuff too, but this I think goes to the root of the question...
4-6-4. HOLDING INSTRUCTIONS
When issuing holding instructions, specify:
a. Direction of holding from the fix/waypoint.
b. Holding fix or waypoint.
NOTE-
The holding fix may be omitted if included at the beginning of the transmission as the clearance limit.
c. Radial, course, bearing, track, azimuth, airway, or route on which the aircraft is to hold.
d. Leg length in miles if DME or RNAV is to be used. Specify leg length in minutes if the pilot requests it or you consider it necessary.
e. Direction of holding pattern turns only if left turns are to be made, the pilot requests it, or you consider it necessary.
PHRASEOLOGY-
HOLD (direction) OF (fix/waypoint) ON (specified radial, course, bearing, track, airway, azimuth(s), or route.)
If leg length is specified,
(number of minutes/miles) MINUTE/MILE LEG.
If direction of turn is specified,
LEFT/RIGHT TURNS.
NOTE-
It is mandatory for the controller to issue left or right turns every time a holding pattern is issued for MLS.
f. Issue maximum holding airspeed advisories when an aircraft is:
1. Approved to exceed the maximum airspeed of a pattern, and is cleared into a holding pattern that will protect for the greater speed; or
2. Observed deviating from the holding pattern airspace area; or
3. Cleared into an airspeed restricted holding pattern in which the icon has not been published.
EXAMPLE-
Due to turbulence, a turboprop requests to exceed the recommended maximum holding airspeed. ATCS may clear the aircraft into a pattern that protects for the airspeed request, and shall advise the pilot of the maximum holding airspeed for the holding pattern airspace area.
PHRASEOLOGY-
"MAXIMUM HOLDING AIRSPEED IS TWO ONE ZERO KNOTS."
regards
Scott