Yes it just means temporary employment through an agency. Most high streets have 2 or 3 agencies and there are also large national ones like Brook Street, Hays, Office Angels. You can usually submit your CV on email or walk into a branch. The agency will usually 'interview' you to understand your skills/experience and what kind of role you are suitable for and then submit you to employers who need temporary staff. Temps are used in most companies to cover roles which are only needed for a short period of time (e.g. to cover a particularly busy time, cover an event, cover sickness absence or holidays of other staff) or to cover for a role in the short term which is being filled permanently in the long term.
The majority of agency work is for low-skill work like retail, warehouse, admin/reception, care work but if you are in a corporate/professional field like IT, finance, HR there are also agencies for these areas. Doing temp work is certainly not a cure for all ills but it can be a good option for those who aren't ready or able to take a permanent role for various reasons or those who find themselves temporarily unemployed whilst looking for permanent work. There are lots of pros and cons...the obvious cons being that as a temp you don't have a guarantee of ongoing work and it can play merry hell with your benefits if you have a fluctuating income. But some pros are:
You usually do lots of short term contracts of anything from a few days to a few months on each 'assignment', so you get to try out a lot of different jobs and different companies which is a plus if you are unsure of your next career move or want to try something different out. If you don't like the job or your manager or colleagues or whatever, you can quickly and easily move on. Con being they can quickly and easily move you on if they don't like you!
Temping can be a good way of building experience on a CV especially for those who have been out of the workplace for a while for whatever reason or who are changing careers. As a manager I am often prepared to take much more of a chance on a temp who doesn't necessarily have good experience because (a) if it doesn't work out they will be moving on at the end of the assignment anyway (b) there is often a shortage of good candidates for temporary roles. The con being that if you are only in the job for a short period of time there would usually be a reluctance to invest as much time and effort in training you as there would be for a permanent person.
Similarly, in my company a lot of temps get taken on as permanent because we've seen their work and know they are good - even if 'on paper' there might be stronger candidates for the permanent role.
In some areas the employment market is very strong for temps, particularly in certain fields, so the money can be good and the temp can pretty much name their terms, so pick their own working hours etc. Not the case universally of course! And also you have to bear in mind that whilst the hourly rate might be good temps don't usually get access to company benefits like the pension scheme and enhanced annual leave, sick pay etc.