I took on the bookkeeping position at my former job, just prior to the firing of the bookkeeper. I knew nothing about the bookkeeping software and had to teach myself the A/R, A/P, payroll and tax payment functions in QuickBooks immediately to stay current. In my other position, I had to teach myself a graphics program to replace one that was becoming non-functional. How do I explain this "self-teaching" on my resume?
The term, as far as I know is - self learning.
In your cover letter, or in the personal summary, you can post this as a skill - you have a couple of very good examples on this.
Self learner - learned the main functions of QuickBooks just prior to the bookkeeper leaving company X. In another job, learnt the XXX graphics program. I can learn new software by myself.
I've never seen this sort of detail listed explicitly; software skills are typically listed in a section on their own, oftentimes categorized by experience ("Expert in A, B, C, Proficient in D, E, F, Familiar with G and H"). I would simply list the software in the appropriate section, and if someone asks how you learned to use the software I would provide the "self learning" answer suggested by Oded.
Have a section on your resume for formal education and applicable skills gained via them.
Next, have a smaller section (just a sentence or two, no fancy formatting or anything) called "Experience With and Knowledge Of:"
and list them there.
In this competitive market, you need to communicate everything you know and they will appreciate it.
Autodidact is a fancy way to describe a "self-learner". Here is an example of how to use it in a sentence:
I am an autodidact and therefore automatically procure the knowledge to update and improve my skill set. This means that company investment in my skill set is never a necessity, although if fore-coming it's always appreciated.
I have demonstrated this in previous roles where I.... blah blah Quickbooks.... blah blah Graphics package.
If applying for a job in the UK, less-complex language that's part of an extended vocabulary can still possess some allure. Take into account your culture when deciding what sort of vocabulary to use. This extended vocabulary is a more interesting and less-dull way of saying you're a self-learner.
If the people you're interviewing know QuickBooks (for instance) then you need to drop a hint about functionality you used that is only in QuickBooks. That way they know you know it. If not, all you can say is 'QuickBooks', since it's not of much interest anyway. If you spent most of your time Invoicing, the emphasis should be on the Invoicing process, not on what software you used. They'll be more interested in knowing whether you can keep track of business details than they are as to what program you did it with.