Down below you can find a list for each ability score in the range of 1-20 with an explanation of each modifiers meaning for a medium sized humanoid. Credit goes to this article for the basis of the following article.
Strength
1 (–5): Morbidly weak, has significant trouble lifting own limbs
2-3 (–4): Needs help to stand, can be knocked over by strong breezes
4-5 (–3): Visibly weak. Might be knocked off balance by swinging something dense
6-7 (–2): Difficulty pushing an object of their weight
8-9 (–1): Has trouble lifting heavy objects for a longer time
10-11 (0): Lifts heavy objects for a short time. Can perform simple physical labor for a few hours without break
12-13 (1): Carries heavy objects and throws small objects for medium distances. Can perform physical labor for half a day without break
14-15 (2): Visibly toned. Carries heavy objects with one arm for longer distances. Doesn’t get too exhausted by physical labor
16-17 (3): Muscular. Can break objects like wood with bare hands and raw strength. Can perform heavy physical labor for several hours without break
18-19 (4): Heavily muscular. Able to out-wrestle a work animal or catch a falling person. Performs the work of multiple people in physical labor
20 (5): Pinnacle of brawn, able to out-lift several people in combined effort.
Dexterity
1 (–5): Barely mobile, probably significantly paralyzed
2-3 (–4): Incapable of moving without noticeable effort or pain
4-5 (–3): Visible paralysis or physical difficulty
6-7 (–2): Significant klutz or very slow to react
8-9 (–1): Somewhat slow, occasionally trips over own feet
10-11 (0): Capable of usually catching a small tossed object
12-13 (1): Able to often hit large targets.
14-15 (2): Able to often hit small targets. Can catch or dodge a medium-speed surprise projectile
16-17 (3): Light on feet, able to often hit small moving targets
18-19 (4): Graceful, able to flow from one action into another easily. Capable of dodging a small number of thrown objects
20 (5): Moves like water, reacting to all situations with almost no effort. Capable of dodging a large number of thrown objects
Constitution
1 (–5): Minimal immune system, body reacts violently to anything foreign
2-3 (–4): Frail, suffers frequent broken bones
4-5 (–3): Bruises very easily, knocked out by a light punch
6-7 (–2): Unusually prone to disease and infection
8-9 (–1): Easily winded, incapable of a full day’s hard labor
10-11 (0): Occasionally contracts mild sicknesses
12-13 (1): Can take a few hits before being knocked unconscious
14-15 (2): Easily shrugs off most illnesses. Able to labor for twelve hours most days
16-17 (3): Able to stay awake for days on end
18-19 (4): Very difficult to wear down, almost never feels fatigue
20 (5): Tireless paragon of physical endurance. Almost never gets sick, even to the most virulent diseases
Intelligence
1 (–5): Animalistic, no longer capable of logic or reason. Behavior is reduced to simple reactions to immediate stimuli
2-3 (–4): Rather animalistic. Acts on instinct but can still resort to simple planning and tactics
4-5 (–3): Very limited speech and knowledge. Often resorts to charades to express thoughts
6-7 (–2): Has trouble following trains of thought, forgets most unimportant things
8-9 (–1): Misuses and mispronounces words. May be forgetful
10-11 (0): Knows what they need to know to get by
12-13 (1): Knows a bit more than is necessary, fairly logical
14-15 (2): Fairly intelligent, able to understand new tasks quickly. Able to do math or solve logic puzzles mentally with reasonable accuracy
16-17 (3): Very intelligent, may invent new processes or uses for knowledge
18-19 (4): Highly knowledgeable, probably the smartest person many people know
20 (5): Famous as a sage and genius. Able to make Holmesian leaps of logic
Wisdom
1 (–5): Seemingly incapable of thought, barely aware
2-3 (–4): Rarely notices important or prominent items, people, or occurrences
4-5 (–3): Seemingly incapable of forethought
6-7 (–2): Often fails to exert common sense
8-9 (–1): Forgets or opts not to consider options before taking action
10-11 (0): Makes reasoned decisions most of the time
12-13 (1): Able to tell when a person is upset
14-15 (2): Reads people and situations fairly well. Can get hunches about a situation that doesn’t feel right
16-17 (3): Often used as a source of wisdom or decider of actions
18-19 (4): Reads people and situations very well, almost unconsciously
20 (5): Nearly prescient, able to reason far beyond logic
Charisma
1 (–5): Barely conscious, probably acts very alien. May have a presence which repels other people.
2-3 (–4): Minimal independent thought, relies heavily on others to think instead
4-5 (–3): Has trouble thinking of others as people and how to interact with them
6-7 (–2): Terribly reticent, uninteresting, or rude
8-9 (–1): Something of a bore, makes people mildly uncomfortable or simply clumsy in conversation
10-11 (0): Capable of polite conversation
12-13 (1): Mildly interesting. Knows what to say to the right people
14-15 (2): Often popular or infamous. Knows what to say to most people and is very confident in debate
16-17 (3): Quickly likeable, respected or feared by many people. May be very eloquent. Good at getting their will when talking to people
18-19 (4): Quickly likeable, respected or feared by almost everybody. Can entertain people easily or knows how to effectively convince them of their own beliefs and arguments
20 (5): Renowned for wit, personality, and/or looks. May be a natural born leader
Inspired by
http://dmingwithcharisma.com/2011/10/dd-stats-in-simple-language/ and
https://www.reddit.com/r/dndnext/comments/81cras/dd_ability_score_ranges_described/