Rec. ITU-T G.100 (11/1988) - DEFINITIONS USED IN FASCICLE III.1
Introduction
1 General terms
    1.1 hypothetical reference connection (HRX)
    1.2 input/output (Recommendations G.111, G.121, etc.)
    1.3 relative level (at a point on a circuit)
    1.4 transmission reference point
    1.5 return loss
2 Transmission performance objectives
    2.1 performance objective
    2.2 design objective
    2.3 commissioning objective
    2.4 limits for maintenance purposes (maintenance limits)
3 Transmission impairments
    3.1 group-delay distortion
    3.2 quantizing distorsion unit (qdu)
4 Propagation time, echo and stability
    4.1 balance return loss
    4.2 echo
    4.3 echo balance return loss
    4.4 echo control device
    4.5 echo loss, L_ECHO
    4.6 talker echo loudness rating (of an international connection)
    4.7 listener echo (receive end echo)
    4.8 listener echo loss (receive echo loss)
    4.9 hollowness
    4.10 open-loop loss (OLL)
    4.11 path a-t-b (transmission loss of . . . ); semi-loop loss
    4.12 stability loss
    4.13 talker echo
    4.14 test balance return loss (TBRL)
    4.15 mean one-way propagation time
5 Equipment
    5.1 R or T pads (in telephone extension)