The medical term for coming into heat is oestrus.
Signs of your cat going into heat are usually fairly obvious.
She will become more affectionate towards you. She’ll often rub her hind quarters against anything available including furniture and you. She will lick her genital area frequently. Her urine will contain more estrogen and the smell will attract male cats and tell them your cat is in heat.
Your cat will raise her rear quarters, her front half lowered and will appear to be walking in place. She will yowl loudly and do this often and for several days.
Cats can go into heat as young as 4 months old and as often as every 3-4 weeks. Of course once she mates this activity will stop.
To prevent your cat going into heat and mating, producing unwanted kittens, it’s best to have her spayed.