Is this considered being a "Tenant", legally? (California)

[Mike Miller]

Without disclosing personal details as to why, basically I am letting a friend's son stay at rental house I have, for free for a bit. I am not charging him rent. He is the only one living there. He is reimbursing me each month for all the utilities, water, electric, and Comcast. 

 I know them, and there is not any issue. But was just curious if he's considered a tenant now, because he's been there 6 months, reimburses me for utilities, and receives mail there. BUT does not technically pay rent, and we've never signed any type of contract or anything. Would he technically still be considered a tenant? 

Thanks