In today's business environment, more and more companies are looking for vendors to help them save time and money. Some services such as phones, technical support and even coffee service are now being outsourced. Managing a vendor's performance can be a difficult task. There must be a way to hold them accountable for the level of service they provide. This accountability comes in the form of a Service Level Agreement, or SLA.
Most Service Agreements will include a SLA. A good SLA will have specific, measurable standards to which the vendor, will be held. The most important parts of the previous sentence are "specific" and "measurable". If the vendor is providing their "standard" SLA, it is highly likely it will be written with a more self-serving slant..
A metric is the specific means by which their service will be measured. These metrics will vary from vendor to vendor depending upon the type of service they are providing. You should go into all negotiations having already defined your own metics to which you will hold the vendor accountable. Many times, you can gauge future interfacing difficulties by the amount of negotiating a vendor will do once your metrics have been defined and presented to them.