In the draft , this is the proposed definition :
"A transport slice is an abstract network topology connecting a number of endpoints, with expected objectives specified through a set of service level objectives (SLO)".

In my view this definition does not report nothing regarding 3 basic concepts related to a "slice": the virtual network ,the related resources providing the requested connectivity to the client, and the SLA/SLO to be matched.
I think in the draft https://www.ietf.org/id/draft-ietf-teas-enhanced-vpn-04.txt
there is a fine definition of transport slice that would be a good reference:
"A transport network slice is a virtual (logical) network with a
particular network topology and a set of shared or dedicated network
resources, which are used to provide the network slice consumer with
the required connectivity, appropriate isolation and specific
Service Level Agreement (SLA) or Service Level Objective (SLO). "

For VN, RFC 8453 reports definition with the two type of possible VN , Type 1 of VN as a set of edge-to-edge abstract links where abstract link is referred to as a VN member formed
as an end-to-end tunnel across the underlying networks or the Type 2, where the connectivity between edge point can be expressed by a set of virtual node and virtual link when more detailed topology is required by client/application .

The abstract link is a representation of the potential to connect a pair of points with certain TE parameters and for all definiton about abstraction RFC7926 can provide details and should be referenced.
I think it should be avoided to introduce another definition when IETF bibliography already provide a reference.

Issue: Line 677 onwards, the definition of NBI and SBI has implementation specific async and bidirectional words. Now a new text is suggested. Please review new text.

TSC Northbound Interface (NBI): The TSC Northbound Interface is a
bidirectional and an asynchronous interface between a higher level
system, e.g. 'E2E network slice orchestrator' and the 'Transport
slice controller'. It is a technology agnostic interface.
---- alternate text ---
TSC Northbound Interface (NBI): is an interface between a higher level
system, e.g. 'E2E network slice orchestrator' and the 'Transport
slice controller'. It is a technology agnostic interface. Over this NBI, slice characteristics and other requirements can be informed to TSC and current state of a transport slice can be retrieved.
--xx--
TSC Southbound Interface (SBI): The TSC Southbound interface is a
bidirectional and an asynchronous interface between 'Transport
slice controller' and network controller(s). These interfaces are
technology-specific and can utilize many of the existing data
models such as L2SM, L3SM, VPN, etc.
----- alternate text -----
TSC Southbound Interface (SBI): is an interface between 'Transport
slice controller' and network controller(s). These interfaces are
technology-specific and can utilize many of the existing data
models such as L2SM, L3SM, VPN, etc. TSC may request network resources or retrieval of their current state.