Pen, an essential writing tool, is a common word in English vocabulary. The word 'pen' is pronounced as /pɛn/ in English.

The pronunciation of 'pen' consists of three phonemes: /p/ , /ɛ/ , and /n/ . The first phoneme /p/ is a voiceless bilabial plosive, which means that the sound is produced by stopping the airflow using both lips and then releasing it explosively. The second phoneme /ɛ/ is an open-mid front unrounded vowel, which is pronounced with the tongue slightly lower and further forward in the mouth than the sound /e/. The last phoneme /n/ is a voiced alveolar nasal, which is produced by bringing the tongue to the alveolar ridge and allowing the voice to pass through the nose.

In American English, the word 'pen' is usually pronounced with a short 'e' sound, which is similar to the sound in 'pet'. However, in British English, the word 'pen' is often pronounced with a long 'e' sound, which is similar to the sound in 'pain'.

In conclusion, the word 'pen' is pronounced /pɛn/ in English, consisting of three phonemes /p/ , /ɛ/ , and /n/. The pronunciation may vary slightly depending on the speaker's accent or dialect.