Linear search is a simple algorithm. It loops through items until the query has been found, which makes it a linear algorithm - the complexity is O(n), where n is the number of items to go through.

Why O(n)? In worst-case scenario, you have to go through all of the n items.

It can be compared to looking for a book in a stack of books - you go through them all until you find the one that you want.

Below is a Python implementation:

```
def linear_search(searchable_list, query):
for x in searchable_list:
if query == x:
return True
return False
linear_search(['apple', 'banana', 'carrot', 'fig', 'garlic'], 'fig') #returns True
```