glotzen
to stare
Colloquial for staring intensely, often rudely or stupidly, at a person or thing.
Hör auf, so zu glotzen, das ist unhöflich!
Stop staring like that, it's rude!

to stare / watch TV
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to stare
Colloquial for staring intensely, often rudely or stupidly, at a person or thing.
Hör auf, so zu glotzen, das ist unhöflich!
Stop staring like that, it's rude!

'Glotzen' (to stare/watch TV) is a very colloquial word and is often used negatively or disparagingly. You should definitely avoid it in formal or polite situations.
Die Kinder haben den ganzen Nachmittag nur geglotzt.
The children just watched TV all afternoon.
The verb 'glotzen' (to stare) is related to the noun 'die Glotzaugen' (bulging/staring eyes), which refers to large, staring eyes. This reinforces the meaning of looking intensely and expressionlessly.
Er stand nur da und glotzte mich mit seinen großen Augen an.
He just stood there and stared at me with his big eyes.
If you want to express that a specific person is being stared at, you can use the separable verb 'anglotzen' (to stare at). The person is then in the accusative.
Der Mann in der U-Bahn hat mich die ganze Zeit angeglotzt.
The man on the subway stared at me the whole time.
In the meaning 'fernsehen' (to watch TV), 'glotzen' is often used in the fixed expression 'in die Glotze glotzen' (to watch the tube). 'Die Glotze' is a colloquial expression for the television.
Ich habe keine Lust auszugehen, ich will nur zu Hause in die Glotze glotzen.
I don't feel like going out; I just want to stay home and watch the tube.
to see
'sehen' and 'glotzen' both have to do with looking. 'sehen' is the neutral word: you perceive something with your eyes or watch a film. 'glotzen' is very colloquial and often negative. It can mean that someone stares for a long time and impolitely, or that someone watches TV passively for a long time. Learners may confuse the words because both describe a kind of looking. But 'glotzen' does not fit in polite or neutral situations. If you do not want a negative tone, use 'sehen'.

Bitte glotz die Leute im Zug nicht so an.
Please don't stare at people on the train like that.
Am Abend sehen wir einen Film im Wohnzimmer.
In the evening, we watch a film in the living room.