a period of time = بُرْهَةٌ
بُرْهَةٌ or بَرْهَةٌ (burhah/barhah) is similar in meaning to مُدَّةٌ (muddah), i.e. a period of time, and many considered the two identical in meaning. The former however is usually used to indicate a relatively long period of time, and is often followed by the phrase مِنَ الدَّهْرِ of time, whereas the latter can be used for either a small or long period of time. So, using them as adverbs of time, مَكَثْتُ بُرْهَةً مِنَ الدَّهْرِ means I stayed for a long time, whereas مَكَثْتُ مُدَّةً means I stayed for some/a period of time.