Add trip definition to general information file

This addresses openmobilityfoundation#748 by adding a definition of a "trip" to the
general-information.md file. The definition is meant for the
purposes of analysis in particular, and not for filtering which
data points are exchanged as part of MDS endpoints.

I wasn't sure on the exact right spot for this since I hadn't seen
anything like this done before in MDS, but I'm open to suggestions
on that and the wording of the definition itself.

general-information.md

@@ -22,6 +22,7 @@ This document contains specifications that are shared between the various MDS AP
   * [Stop Status](#stop-status)
   * [GBFS Compatibility](#gbfs-compatibility)
 * [Timestamps](#timestamps)
+* [Trips](#trips)
 * [UUIDs](#uuids)
 * [Vehicle States](#vehicle-states)
   * [Event Types](#event-types)
@@ -177,6 +178,25 @@ Note if implementing the beta feature [Geography Driven Events](/general-informa
 
 [Top][toc]
 
+## Trips
+
+Counting trips is a common analysis with MDS data, but in some instances when
+a user rents a vehicle the rental may end up being very short because the
+vehicle is unusable or because the customer changes their mind.
+To facilitate a common definition of trips for analysis, MDS defines a trip
+as a user taking control of a vehicle for 60 seconds or more.
+If a user reserves a vehicle and cancels before taking control of the vehicle
+that reservation does not count as a trip, nor does a user taking control of
+the vehicle and canceling or ending the trip in under 60 seconds.
+
+Providers are still expected to report these events in MDS endpoints,
+but parties may use this definition as a shared reference at the
+recommendation of the MDS community.
+
+For reference on the development of this definition please refer to
+[issue #748](https://github.com/openmobilityfoundation/mobility-data-specification/issues/748)
+in the MDS Github repository.
+
 ## Propulsion Types
 
 | `propulsion`      | Description                                            |