"Array" can be defined as "to place in an orderly arrangement". It is important that the gene sequences in a microarray are attached to their support in an orderly or fixed way, because a researcher uses the location of each spot in the array to identify a particular gene sequence. The spots themselves can be DNA, cDNA, or oligonucleotides. Microarrays can be broadly defined as " tools for massively paralleled ligand binding assays where features (e.g. oligonucleotides) are placed on a solid support (e.g a glass slide) at high density for recognising a complex mixture of target molecules."