What is meant by basal level transcription?

Basal level transcription is the transcription of genes necessary for some basal functions of the cell (cell respiration, cell metabolism, etc). This basal level transcription is characteristic for every cell in the organism - brain cells, liver cells, muscle cells, etc. It is important that every basal function of each cell in the organism remains same and in the homeostasis. Transcription of genes other from those important for basal functions occurs in tissue-specific, time-specific manner.