Fiqh: literally means to understand and comprehend.
Allah says in the Quran Majeed:

قَالُوا يَا شُعَيْبُ مَا نَفْقَهُ كَثِيرًا مِمَّا تَقُولُ

“They said, O Shuaib! We do not understand (نفقه) much of what you are saying.”
In another place of the Quran Majeed, Allah Ta’laa says:

وَمَا كَانَ الْمُؤْمِنُونَ لِيَنْفِرُوا كَافَّةً ۚ فَلَوْلَا نَفَرَ مِنْ كُلِّ فِرْقَةٍ مِنْهُمْ طَائِفَةٌ لِيَتَفَقَّهُوا فِي الدِّينِ وَلِيُنْذِرُوا قَوْمَهُمْ إِذَا رَجَعُوا إِلَيْهِمْ لَعَلَّهُمْ يَحْذَرُونَ

“It is not for the Believers to go forth all together. If a contingent from every expedition go forth to devote themselves to understanding the religion, (ليتفقهوا في الدين) and warn their people when they return to them, so they (may learn) to guard themselves (against evil).” (9 : 122)
Saiyiduna Muawiyah (may Allah be pleased with him) said, ‘I heard the Messenger of Allah (صلى الله عليه وسلم) saying:

 من يرد الله به خيرا يفقهه في الدين

“For whomsoever Allah intends an abundant good, He grants him the understanding of the Deen (religion).” (Bukhari 71)
Therefore “fiqh” is the understanding of any aspect of the Deen, whether it is an issue of theology, tafsir, hadith, jurisprudence or tazkiyah.
And Allah knows best.