In Dungeons & Dragons, a player can choose to, amongst many other things, climb a wall, push open a door, or jump across an impediment. These actions are considered to be strength based abilities, with the 5e Player’s Handbook saying that (p.175, 2014):
Strength measures bodily power, athletic training, and the extent to which you can exert raw physical force.
To check whether or not the player’s character successfully makes that climb, push, or jump, the dungeon master (DM) will have the player make a strength ability check by rolling the die. Based on what the character’s strength is, they will have a strength modifier which will be added to the number they roll with the die. This total number will dictate whether or not they successfully achieved their feat of strength or just fell flat on their face.
Now, whether or not we play as characters with a high strength ability, we all need strength to keep standing, walking, picking things up, etc. well into old age. Because of this need for strength, the American College of Sports Medicine recommends that it is essential that we all get the equivalent of at least two total body strength training sessions in each week (if you split up strength training by focusing on different body areas on different days, then you’ll be strength training more than twice a week).