ERCC or spike-in
External RNA Control Consortium (ERCC) or spike-in controls are a set of nucleic acid fragments with a conventional sequence. They resemble natural eukaryotic mRNAs. Added in a known quantity to the sample, they establish a baseline measurement. In this way, ERCCs can be used to calibrate measurements and to monitor technical variation.
Unique Molecular Identifier (UMI)
UMIs are molecular barcodes used to uniquely tag each RNA molecule in a sample. In the resulting dataset, they represent reads or transcripts. UMIs are short DNA sequences with random bases. The number of bases is chosen such that the number of distinct UMIs exceeds the number of unique RNA molecules. After PCR amplification, the distinct RNA molecules can be traced back using UMIs.