heiß
hot
Having a high temperature. Describes things that feel very warm or have a high degree value.
Vorsicht, der Kaffee ist noch sehr heiß!
Careful, the coffee is still very hot!

hot
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hot
Having a high temperature. Describes things that feel very warm or have a high degree value.
Vorsicht, der Kaffee ist noch sehr heiß!
Careful, the coffee is still very hot!

To express that you feel the ambient temperature is high, use the dative construction 'Mir ist heiß' (I am hot / I feel hot). The sentence 'Ich bin heiß' means colloquially that you consider yourself sexually attractive (meaning m03). This is a very common mistake.
Kannst du das Fenster öffnen? Mir ist so heiß.
Can you open the window? I am so hot.
The adjective 'heiß' (hot) belongs to the word family around the noun 'die Hitze' (heat). When you learn 'heiß', learn 'die Hitze' at the same time to expand your vocabulary.
Bei dieser Hitze sollte man viel trinken.
In this heat, you should drink a lot.
In the figurative meaning 'intensiv' (intense), 'heiß' (hot/heated) is often combined with abstract nouns that describe a conflict or a decisive phase. Typical examples are 'eine heiße Debatte' (a heated debate), 'eine heiße Phase' (a crucial/intense phase), or 'ein heißer Kampf' (a fierce battle).
Das Projekt geht jetzt in die heiße Phase.
The project is now entering the crucial phase.
The meaning 'sexuell attraktiv' (sexually attractive) is strongly colloquial. In formal or neutral conversations, you should avoid this use because it can seem too direct or inappropriate.
Meine kleine Schwester findet den Schauspieler total heiß.
My little sister thinks the actor is totally hot.
The combination 'heiß begehrt' (hotly desired / in high demand) is a fixed expression and means that something is very sought after and popular. It is often used for products, jobs, or university places.
Die Plätze in diesem Studiengang sind heiß begehrt.
The places in this degree program are in high demand.
The expression 'ein heißer Tipp' (a hot tip) is a fixed expression for especially good and often exclusive advice. You can 'give' or 'get' a hot tip.
Ein Freund gab mir den heißen Tipp, mich auf diese Stelle zu bewerben.
A friend gave me the hot tip to apply for this position.
cold
'heiß' and 'kalt' are opposites when talking about temperature. 'heiß' is used for something with a high temperature that feels very warm or can even be dangerous. 'kalt' is used for something with a low temperature. This contrast is important in many everyday situations, for example with drinks, food, water, or weather. So you say 'heißer Tee' (hot tea) when the tea is very warm, and 'kaltes Wasser' (cold water) when the water has a low temperature.

Pass auf, die Pfanne ist noch sehr heiß.
Be careful, the pan is still very hot.
Nach dem Training trinkt sie ein kaltes Wasser.
After training, she drinks some cold water.