die Flasche
bottle
A container, usually made of glass or plastic, with a narrow neck, used for storing liquids.
Könntest du mir bitte eine Flasche Wasser aus dem Kühlschrank holen?
Could you please get me a bottle of water from the fridge?

bottle
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bottle
A container, usually made of glass or plastic, with a narrow neck, used for storing liquids.
Könntest du mir bitte eine Flasche Wasser aus dem Kühlschrank holen?
Could you please get me a bottle of water from the fridge?

You can recognize the meaning from the context. Most of the time, it means the container for liquids. If someone is talking about a person and the tone is negative, it is the insult. Words like 'Gas' (gas), 'Sauerstoff' (oxygen), or 'Druck' (pressure) point to the container for gas.
Stell die Flasche Milch bitte zurück in den Kühlschrank.
Please put the bottle of milk back in the fridge.
Using 'Flasche' (bottle/loser) to refer to a person is very colloquial and insulting. It means calling someone a failure or an incapable person.
Nimm den Ball weg, du Flasche, du triffst ja nicht mal das Tor!
Give up the ball, you loser—you can't even hit the goal!
The insult became very well known through the football coach Giovanni Trapattoni. In a famous press conference, he shouted about a player: 'Flasche leer!' (Bottle empty!). Since then, the expression 'Flasche' (loser/useless person) has been very popular for a bad player in sports.
Seit seinem Fehler im Spiel wird er von den Fans als „Flasche“ beschimpft.
Since his mistake in the game, the fans have been insulting him by calling him a 'Flasche' (loser).
In the meaning of 'container for gas,' 'Flasche' (cylinder) is often used as part of a compound noun, e.g. 'Gasflasche' (gas cylinder), 'Sauerstoffflasche' (oxygen cylinder), or 'Druckluftflasche' (compressed-air cylinder).
Für den Campingausflug brauchen wir eine neue Gasflasche.
We need a new gas cylinder for the camping trip.
jug / inn
'die Flasche' and 'der Krug' are both containers for liquids. A bottle usually has a narrow neck and is often closed, for example for water, juice, or oil. A jug is usually more rounded, has a handle, and is used more for pouring, for example with water or beer. The words can be confused because both can hold liquids. If you pour from it and it has a handle, 'Krug' often fits better; for a narrow container with a lid or cork, 'Flasche' fits.

Für die Wanderung packt Max eine große Flasche Wasser ein.
Max packs a large bottle of water for the hike.
Auf dem Tisch stand ein Krug mit frischem Apfelsaft.
There was a jug of fresh apple juice on the table.