As the previous posts state, the short answer to your question is that strength training is training where your muscles are working against a resistance. Even though a lot of people see strength training as being the same as weight-lifting, it isn’t necessarily the same. Strength or resistance training is a broader concept in that it can literally involve any kind of resistance (e.g. resistance bands, elastic tubes, body weight etc.).
Strength training can involve several different methods, depending on your goals. For example you will train differently if you want to build strength endurance (being able to perform work that requires a certain level of strength over a period of time) than you would if you simply want to increase your raw or one-repetition maximum strength (training to lift or otherwise move the most weight you can).
Also there is a difference between “relative” strength (a person’s strength relative to their size) versus “raw” strength (simply looking at how strong a person is irrespective of their size).
So as you can see, while strength training itself is a fairly simply concept how you actually train to improve your strength will depend on several factors including the reasons why you’re strength training. I hope this helps!
The 5th edition of the Fitness Professionals Handbook authored by Edward T. Howley and B. Franks define strength as “the maximal force that a muscle or muscle group can generate at a specified velocity.”
Resistance training accord to the above-mentioned authors is a “method of conditioning designed to increase a person’s ability to exert or resist force.”
That being said, there is a difference between resistance training and strength training. The training adaptation one gets from “strength training” is very different from the training adaptation I would get if I am training for hypertrophy.
Its the difference between an Olympic power lifter (who trains for strength and and someone doing biceps curls with a five pound weight. The load makes a big difference. One is maximal the other is not.
Hope this helps.
Here is what I wrote in response to Bryant Seton:
I take it seriously, because my new client got a recommendation to incorporate strength training and had NO idea what he meant. She is 70 and has not exercised other then walking. On the other hand the person asking is a fitness instructor looking at her profile.