In an RNA microarray, a hybridization event between a probe and target sequence would indicate a presence of the transcript within the sample. The probes are oligonucleotide sequences found on the microarray chip. The target sequences are representative of the entire transcriptome. The targets are found within your biological sample and have gone through many rounds of amplification in addition to labeling with fluorescent dyes. The fluorescently labeled target when bound to the probe can then be detected using a scanning laser.