Broadly speaking, the term 'communications technology' can refer to any technology that allows its users to communicate with one another. Using this (allowedly loose) definition, two-way radios and mobile phones fall into the category of 'communications technology'.
The term also refers to computers and computer-related work. Here in the UK, schools study a subject called 'ICT' this stands for 'Information and Technology' (although this rapidly aging writer was at school, it was simply known as 'IT' or, 'Information Technology').
As the Internet has become a more and more prevalent part of our society, communications over longer distances have become significantly easier. In fact, these types of communications are easier now than at any other time in Human history. Ergo, it stands to reason that computers should be considered as a prime form of communications technology.
Basic, everyday acts such as checking your emails, updating your Facebook or Twitter feed, answering the phone, or taking Skype calls are all a part of 'communications technology' as are the two-way radios used by public transport, security firms and the emergency services.
A person who makes a living by working with 'comms tech' is likely involved in the designing, creating, implementing or maintaining of communicational systems. Such systems can include radio networks, mobile phone providers, telephone companies, even television. It is a broad and ever-expanding field, which makes it difficult to ascertain exactly what a person actually does if they list it as their job title.
When someone tells you that they are a plumber, for example, you get a broad idea of what they do for a living all day. If I tell you that I am a professional copywriter, you at least have some notification as to what that entails. A person who works in the field of 'comm tech' could be doing almost anything.
In case you're wondering, the Internet itself can be considered as a communication technology, given that any person who uploads videos or writes blogs is reading the very videos that are watched.
Telecom's is a huge field and, as I think you'll agree, a pretty important one. Without the ability to communicate with others, either through short distances on your mobile or much longer distances (such as the distance between our office in the UK and your home on the African continent), this world would be a vastly different place.