Credit

A credit was a generic term for a monetary unit. Many worlds and civilisations described their money with the term. While they were not the same system, they often (but not always) referred to a currency system that operated electronically, rather than using currency (i.e., notes and coins).

Human usage
In the year 2050 credits (sometimes called "creds") were the currency in Department-controlled Britain. (TV: The Custodians, Oroborus) By 2062 the UK no longer used credits and had switched to the Euro. (PROSE: The Last Dodo)

River Song was contracted for four million credits by DreamInc to help design New Venice. (PROSE: Death in New Venice)

In the 42nd century (approximately year 4126), in the Second Great and Bountiful Human Empire, the price of an Ood slave was 50 credits. (TV: Planet of the Ood)

Also during the 42nd century, Panda bought two luxury towels from a branch of Cosmomart on Trull for 4000 credits. (AUDIO: The Iris Wildthyme Appreciation Society)

In the year 200,000, a Kronkburger on-board Satellite Five cost 2 credits 20. A head chip cost 100 credits and a full Infospike cost 10,000 credits. (TV: The Long Game) A hundred years later, Rodrick won a reward of 1600 credits "courtesy of the Bad Wolf Corporation" on The Weakest Link, only to be exterminated by the Daleks before he could receive it. (TV: Bad Wolf / The Parting of the Ways)

On the Chasm Forge mining station, humans had to pay credits to receive oxygen. (TV: Oxygen)

On New Earth, in 5,000,000,053, one patch of Forget 43 cost two credits. (TV: Gridlock)

A Beta Dart spacecraft was known to cost upwards of 1 million credits depending on the fittings. (TV: The Space Pirates)

Other species
The Stoish civilisation had credits which were stored on "credit cards". The Tenth Doctor said that £1,000,000 was equal to 50,000,056 credits in the early 21st century. (TV: Voyage of the Damned)

The Inter Minorians and Lurmans used credit bars that were blue. One bar represented one credit. (TV: Carnival of Monsters)

A slave trade species in the future only accepted galactic credits as payment. (COMIC: Prisoners of Time)

When the Gaztak mercenary Grugger prepared to strip Meglos's ships for parts, he asked his aid Brotodac how much he thought the console "would fetch on Pelagos". Brotodac guessed "five million credits." (PROSE: Meglos)