Common symbol for 1,500 volts.

Common symbol for 25,000 volts.

Common symbol for 50 volts.

Common symbol for 750 volts.

The rail operator is typically responsible for everything "above" where the wheels of a train makes contact to the rail. "Above rail" includes the rolling stock, scheduling and operation of services, selling tickets, staffing stations, etc. 

The track manager is typically responsible for everything "below" where the wheels of a train makes contact: the track infrastructure. This includes the track, signalling equipment and other infrastructure (including any overhead traction supply).

See also below rail.

An absolute signal is signal that a driver must not pass when at danger (stop) without special permission.

This is different to the possible actions for a permissive signal.

ac = alternating current, as found in the household electricity supply

The Australian Qualifications Framework (commonly known as the AQF) is a unified system of national qualifications in schools, vocational education and training (TAFEs and private providers) and the higher education sector (mainly universities).

The qualifications are:

Senior Secondary Certificate of Education;
Certificate I;
Certificate II;
Certificate III;
Certificate IV;
Diploma, Advanced Diploma;
Associate Degree;
Bachelor Degree;
Vocational Graduate Certificate;
Vocational Graduate Diploma;
Graduate Certificate;
Graduate Diploma;
Masters Degree;
Doctoral Degree.

More information: http://www.aqf.edu.au/aboutaqf.htm

Australian Quality Training Framework

The Australian Quality Training Framework (AQTF) provides the basis for Australia's nationally consistent, high quality vocational education and training system.

The nationally agreed quality arrangements for the Vocational Education and Training (VET) system, as agreed to by the Ministerial Council.