What is it

It is much faster to issue 1 query that returns 100 results than to issue 100 queries that each return 1 result.

Solution

Typically be avoided by doing a join in your query to force-fetch all the data you need in one go.

Illustration

# N+1 Queries for 4 matching records (1+4 = 5 queries total)
SELECT
    pc.id AS id,
    pc.review AS review,
    pc.post_id AS postId
FROM post_comment pc

SELECT p.title FROM post p WHERE p.id = 1
SELECT p.title FROM post p WHERE p.id = 2
SELECT p.title FROM post p WHERE p.id = 3
SELECT p.title FROM post p WHERE p.id = 4

# Extract all the data you need in the SQL query at once (1 query)
SELECT
    pc.id AS id,
    pc.review AS review,
    p.title AS postTitle
FROM post_comment pc
JOIN post p ON pc.post_id = p.id