1. Messenger RNA (mRNA): Carries genetic information from DNA in the nucleus to the ribosomes in the cytoplasm, where proteins are synthesized.

2. Transfer RNA (tRNA): Brings amino acids to the ribosomes during protein synthesis, matching them to the codons on mRNA.

3. Ribosomal RNA (rRNA): Forms the structural and catalytic core of ribosomes, the cellular machinery responsible for protein synthesis.

In addition to these three main types, there are also other, less common types of RNA, including:

* Small nuclear RNA (snRNA): Involved in splicing, the process of removing non-coding sequences from pre-mRNA.

* Small nucleolar RNA (snoRNA): Involved in the processing and modification of rRNA.

* MicroRNA (miRNA): Regulates gene expression by binding to mRNA and inhibiting translation.

* Small interfering RNA (siRNA): Similar to miRNA, but typically targets specific mRNA sequences for degradation.

* Long non-coding RNA (lncRNA): Diverse roles in gene regulation, cell differentiation, and other cellular processes.

The exact number of RNA types can vary depending on how you define "type," as there is a diverse range of RNA molecules with specific functions. However, the three main types (mRNA, tRNA, and rRNA) are fundamental for cellular processes.