A welder is someone who welds for a living; welding is a craft in which pieces of material are joined together. Classically, welding has been accomplished in metals, but modern welders also work with plastics. The term “welder” is also used to describe equipment used in the process of welding; some people use the term “weldor” to talk about someone who welds so that the distinction is clear.
Welding is an ancient profession. People have been working with metals for thousands of years, and metalworking is such an important part of human life that archaeologists even use the working of various metals to describe eras in human history like the Bronze and Iron Ages. Classically, welding has been accomplished with the use of heat to melt the metals before joining them together; modern welding includes an assortment of other techniques for joining material, including electricity in arc welding and ultrasound, which is used to join many plastics.
Many welders work in heavy industry, since welding is a crucial stage in the construction of things like cars, trains, and ships, along with industrial equipment. Welders can also work in lighter industry, or as freelance contractors who fix various metal objects. The construction industry also employs a lot of welders, as many buildings use heavy duty metal framework to support themselves, and this framework must be assembled and secured by welders.
There are two basic ways to train to be a welder. Some welders attend trade schools which offer anywhere from weeks to years of training to students, depending on how specialized they want to get. Others apprentice, getting on the job training from experienced welders. One of the advantages of trade school is that welders can learn about cutting edge techniques which may not have been perfected in the field yet, although welders who apprentice are paid as they learn, which can be an important consideration for some aspiring welders.
In order to become a welder, someone needs to be reasonably strong, especially in heavy industry, because he or she will have to work with heavy materials. It also helps to be extremely observant and dexterous, as welders sometimes need to think fast and they work with very hot, dangerous materials. Having a passion for and an interest in metals is not a requirement, but it is certainly useful, and knowing your field of interest before you train can be useful. For example, a welder might be interested in working in a shipyard or in a company which works with plastics, and these two types of welding require very different skills.