Creepage с расстоянием в оптоэлектронике

[vvin]

Подскажите как расшифровывается creepage в этой фразе:
Optocoupler is housed in a stretched SO-8 package and provides 8 mm creepage and 8 mm clearance which reduces up to 40% of board design space versus standard 300 mil DIP packages.

[alk]

http://catalog.gaw.ru/index.php?page=component_detail&id=4931
http://catalog.gaw.ru/index.php?page=document&id=4616
в англоязычном pdf'е (стр.5)
Minimum External Air Gap (Clearance)
Measured from input terminals to output terminals, shortest distance through air.
Minimum External Tracking (Creepage)
Measured from input terminals to output
terminals, shortest distance path along body.
...
For creepage, the shortest distance path along the surface of a printed circuit board between the solder fillets of the input and output leads must be considered.

Отсюда
http://www.multitran.ru/c/m.exe?l1=1&l2=2&shortf=1&s=creepage+distances
и наконец
https://library.abb.com/GLOBAL/SCOT/SCOT209.nsf/VerityDisplay/D2C596177F06A419C1257274003AABBD/$File/1TFC902006B1101.pdf
стр.13 см. рисунок
clearance - Воздушный зазор
creepage distance - Длина пути утечки