when state colon is not there in syntax its giving an error in QueueableApex in Salesforce?

List<Account> ListAccount = [SELECT ID, Name ,(Select id,FirstName,LastName from contacts ) FROM ACCOUNT WHERE BillingState = :state LIMIT 200];

Here my question is before state colon is there does it mean to be syntax or something else because removing it giving an error!

• This discussion was modified 6 years, 3 months ago by  Deepak.
• This discussion was modified 6 years, 3 months ago by  Forcetalks.
• This discussion was modified 6 years, 3 months ago by  Forcetalks.