In REST API Metadata what does updatable= FALSE means?

Summary:

In REST API Metadata what does updatable= FALSE means?

Content (required):

We can get any REST API Metadata by using "Rest URL/Describe"

example - https://hostname.com/fscmRestApi/resources/latest/standardReceipts/describe

In the metadata(The response which we receive from above) we can see the column specification like below:

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"attributes" : [ {

    "name" : "StandardReceiptId",

    "type" : "integer",

    "updatable" : true,

    "mandatory" : true,

    "queryable" : true,

    "allowChanges" : "inCreate",

    "precision" : 18,

    "hasDefaultValueExpression" : true,

    "title" : "Standard Receipt ID",

    "properties" : {

     "fnd:GLOBALLY_UNIQUE" : "true"

    },

Question is what does "updatable" : true/false means?

The observation is -> If i pass the attribute which is marked as "Updatable": false ,