Dimensions: Dimensions are used to break down your key metrics into different segments.
The most common dimensions include your funnel type (eg Inbound/Outbound), region, attribution, and industry.
The dimensions applied to a key metric define its segment.
Segments: A segment is the set of dimensions that defines a metric.
For example, you may have used the dimensions: revenue stream and regions in your GTM engine.
Looking at your engine, you see Opportunities with the dimensions Outbound and EMEA assigned → The combination of Outbound and EMEA is your segment.