A single contextfree language can be expressed by more than one contextfree grammar(CFG). There are two types of equivalent when comparing grammars:

Two grammars are weakly equivalent if they generate the same strings

Two grammars are strongly equivalent if they generate the same strings via the same derivations
Chomsky Normal Form
In Chomsky Normal Form (CNF), the RHS of every production rule includes either two nonterminals or a single terminal symbol: A –> BC or A –> a.
All CFGs can be turned into a weakly equivalent CNF grammar. To do so, we would need to create a new “dummy” nonterminals to address production rules with more than two nonterminals. For example, converting W –> X Y Z to W –> X W\X and W\X –> Y Z.
In this case, W\X is the new dummy nonterminal. This step binarises the grammar, which is important for bottomup parsing. Production rules with RHS that contains a mix of terminal and nonterminal symbols can be replaced using similar approach. Unary nonterminal productions A –> B are replaced as follows: for each production B –> alpha in the grammar, add a new production rule A –> alpha. However, we would still keep the production rule A –> B since it is a valid binary production.