A profit is where you make more money than the cost to run the blog.
So for me It was costing me $5.00 per month for hosting my blog and then another $10.00 per year for the domain so total cost per month to host the blog for me was around roughly $5.75 per month including the domain cost.
So once I started getting 30,000 monthly visitors I started making from $10.00 to $20.00 per month blogging from Adsense.
Now that's not a good income but it's profit since I had money leftover after paying the hosting and domain cost for the blog.
Once I started getting up to 120,000 monthly unique visitors to the blog then I started earning from $200.00 to $300.00 per month from Adsense.
It wasn't until my blog started getting 300,000 monthly unique visitors then my blog started making me $800.00 to $1,000.00 per month.